sim: formally assume unistd.h always exists (via gnulib)

We have many uses of unistd.h that are unprotected by HAVE_UNISTD_H,
so this is more formalizing the reality that we require this header.
Since we switched to gnulib, it guarantees that a unistd.h exists
for us to include, so we're doubly OK.
diff --git a/sim/arm/armos.c b/sim/arm/armos.c
index a8ef7e4..9cf238a 100644
--- a/sim/arm/armos.c
+++ b/sim/arm/armos.c
@@ -31,10 +31,7 @@
 #include <errno.h>
 #include <limits.h>
 #include <string.h>
-
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>		/* For SEEK_SET etc.  */
-#endif
 
 #include "armdefs.h"
 #include "armos.h"
diff --git a/sim/common/callback.c b/sim/common/callback.c
index ff14a11..306e95e 100644
--- a/sim/common/callback.c
+++ b/sim/common/callback.c
@@ -34,9 +34,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <sys/stat.h>
 #include <sys/types.h>
 
diff --git a/sim/common/dv-pal.c b/sim/common/dv-pal.c
index 56692c1..25f8c68 100644
--- a/sim/common/dv-pal.c
+++ b/sim/common/dv-pal.c
@@ -24,9 +24,7 @@
 
 #include <stdlib.h>
 #include <string.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 
 #include "sim-main.h"
 #include "hw-main.h"
diff --git a/sim/common/dv-sockser.c b/sim/common/dv-sockser.c
index fba2775..698cab8 100644
--- a/sim/common/dv-sockser.c
+++ b/sim/common/dv-sockser.c
@@ -29,9 +29,7 @@
 #include <signal.h>
 #include <stdlib.h>
 #include <string.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <arpa/inet.h>
 #include <netinet/in.h>
 #include <sys/select.h>
diff --git a/sim/common/nrun.c b/sim/common/nrun.c
index 4c01162..2ebf8a1 100644
--- a/sim/common/nrun.c
+++ b/sim/common/nrun.c
@@ -21,10 +21,8 @@
 #include <stdlib.h>
 /* For strsignal.  */
 #include <string.h>
-#ifdef HAVE_UNISTD_H
 /* For chdir.  */
 #include <unistd.h>
-#endif
 
 #include "bfd.h"
 #include "environ.h"
diff --git a/sim/common/sim-io.c b/sim/common/sim-io.c
index f126c96..fc0d42f 100644
--- a/sim/common/sim-io.c
+++ b/sim/common/sim-io.c
@@ -29,9 +29,7 @@
 #include <stdarg.h>
 #include <stdint.h>
 #include <stdlib.h>
-#if HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 
 #undef open
 
diff --git a/sim/common/sim-memopt.c b/sim/common/sim-memopt.c
index 2d1b96b..2e5016c 100644
--- a/sim/common/sim-memopt.c
+++ b/sim/common/sim-memopt.c
@@ -26,9 +26,7 @@
 #endif
 #include <stdlib.h>
 #include <string.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #ifdef HAVE_SYS_MMAN_H
 #include <sys/mman.h>
 #endif
diff --git a/sim/common/syscall.c b/sim/common/syscall.c
index f65f616..96033db 100644
--- a/sim/common/syscall.c
+++ b/sim/common/syscall.c
@@ -33,9 +33,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <sys/stat.h>
 #include <sys/types.h>
 
diff --git a/sim/configure b/sim/configure
index c1333fc..1047514 100755
--- a/sim/configure
+++ b/sim/configure
@@ -2797,7 +2797,6 @@
 as_fn_append ac_header_list " fcntl.h"
 as_fn_append ac_header_list " fpu_control.h"
 as_fn_append ac_header_list " termios.h"
-as_fn_append ac_header_list " unistd.h"
 as_fn_append ac_header_list " utime.h"
 as_fn_append ac_header_list " linux/if_tun.h"
 as_fn_append ac_header_list " linux/mii.h"
@@ -5268,8 +5267,6 @@
 
 
 
-
-
   for ac_func in $ac_func_list
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
@@ -12289,7 +12286,7 @@
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12292 "configure"
+#line 12289 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12395,7 +12392,7 @@
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12398 "configure"
+#line 12395 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
diff --git a/sim/cr16/simops.c b/sim/cr16/simops.c
index e652b81..73420a7 100644
--- a/sim/cr16/simops.c
+++ b/sim/cr16/simops.c
@@ -24,9 +24,7 @@
 #include <errno.h>
 #include <sys/types.h>
 #include <sys/stat.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <string.h>
 #include <time.h>
 #include <sys/time.h>
diff --git a/sim/cris/dv-rv.c b/sim/cris/dv-rv.c
index 6caa4dd..9142b88 100644
--- a/sim/cris/dv-rv.c
+++ b/sim/cris/dv-rv.c
@@ -29,9 +29,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <string.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <stdlib.h>
 #ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>
diff --git a/sim/cris/rvdummy.c b/sim/cris/rvdummy.c
index a263ee3..91a7ddc 100644
--- a/sim/cris/rvdummy.c
+++ b/sim/cris/rvdummy.c
@@ -36,10 +36,7 @@
 #include "libiberty.h"
 
 #include <stdio.h>
-
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <stdlib.h>
 #include <string.h>
 #ifdef HAVE_SYS_TYPES_H
diff --git a/sim/cris/traps.c b/sim/cris/traps.c
index afcb348..f5f169f 100644
--- a/sim/cris/traps.c
+++ b/sim/cris/traps.c
@@ -32,9 +32,7 @@
 #include <stdlib.h>
 #include <stdarg.h>
 #include <errno.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #ifdef HAVE_FCNTL_H
 #include <fcntl.h>
 #endif
diff --git a/sim/d10v/simops.c b/sim/d10v/simops.c
index 96ed29f..bc7806c 100644
--- a/sim/d10v/simops.c
+++ b/sim/d10v/simops.c
@@ -5,9 +5,7 @@
 #include <errno.h>
 #include <sys/types.h>
 #include <sys/stat.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <string.h>
 
 #include "bfd.h"
diff --git a/sim/m4/sim_ac_platform.m4 b/sim/m4/sim_ac_platform.m4
index 6356a80..665c1bd 100644
--- a/sim/m4/sim_ac_platform.m4
+++ b/sim/m4/sim_ac_platform.m4
@@ -18,12 +18,12 @@
 [dnl
 dnl Check for common headers.
 dnl NB: You can assume C11 headers exist.
+dnl NB: We use gnulib from ../gnulib/, so we don't probe headers it provides.
 AC_CHECK_HEADERS_ONCE(m4_flatten([
   dlfcn.h
   fcntl.h
   fpu_control.h
   termios.h
-  unistd.h
   utime.h
   linux/if_tun.h
   linux/mii.h
@@ -46,6 +46,7 @@
 ]))
 AC_HEADER_DIRENT
 
+dnl NB: We use gnulib from ../gnulib/, so we don't probe functions it provides.
 AC_CHECK_FUNCS_ONCE(m4_flatten([
   __setfpucw
   access
diff --git a/sim/m68hc11/emulos.c b/sim/m68hc11/emulos.c
index 50d2753..fcf9cc1 100644
--- a/sim/m68hc11/emulos.c
+++ b/sim/m68hc11/emulos.c
@@ -21,9 +21,7 @@
 #include "defs.h"
 
 #include "sim-main.h"
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 
 #include "m68hc11-sim.h"
 
diff --git a/sim/mn10300/op_utils.c b/sim/mn10300/op_utils.c
index b29b803..7e035f4 100644
--- a/sim/mn10300/op_utils.c
+++ b/sim/mn10300/op_utils.c
@@ -3,9 +3,7 @@
 
 #include <errno.h>
 #include <time.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/time.h>
diff --git a/sim/ppc/emul_bugapi.c b/sim/ppc/emul_bugapi.c
index f4eed44..067e406 100644
--- a/sim/ppc/emul_bugapi.c
+++ b/sim/ppc/emul_bugapi.c
@@ -27,9 +27,7 @@
 #include "emul_generic.h"
 #include "emul_bugapi.h"
 
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <stdlib.h>
 #include <string.h>
 
diff --git a/sim/ppc/emul_chirp.c b/sim/ppc/emul_chirp.c
index 116f373..c064a28 100644
--- a/sim/ppc/emul_chirp.c
+++ b/sim/ppc/emul_chirp.c
@@ -28,9 +28,7 @@
 #include "emul_chirp.h"
 
 #include <string.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 
 #ifndef STATIC_INLINE_EMUL_CHIRP
 #define STATIC_INLINE_EMUL_CHIRP STATIC_INLINE
diff --git a/sim/ppc/emul_netbsd.c b/sim/ppc/emul_netbsd.c
index a8bfd27..51f8e98 100644
--- a/sim/ppc/emul_netbsd.c
+++ b/sim/ppc/emul_netbsd.c
@@ -72,10 +72,8 @@
 # endif
 #endif
 
-#ifdef HAVE_UNISTD_H
 #undef MAXPATHLEN		/* sys/param.h might define this also */
 #include <unistd.h>
-#endif
 
 #include <stdlib.h>
 
diff --git a/sim/ppc/emul_unix.c b/sim/ppc/emul_unix.c
index 1d8b781..2872d23 100644
--- a/sim/ppc/emul_unix.c
+++ b/sim/ppc/emul_unix.c
@@ -115,10 +115,8 @@
 # endif
 #endif
 
-#ifdef HAVE_UNISTD_H
 #undef MAXPATHLEN		/* sys/param.h might define this also */
 #include <unistd.h>
-#endif
 
 #include <stdlib.h>
 #include <time.h>
diff --git a/sim/ppc/hw_com.c b/sim/ppc/hw_com.c
index 4ffd732..768d1ca 100644
--- a/sim/ppc/hw_com.c
+++ b/sim/ppc/hw_com.c
@@ -28,9 +28,7 @@
 #include "device_table.h"
 
 #include <string.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <stdlib.h>
 
 /* DEVICE
diff --git a/sim/ppc/hw_disk.c b/sim/ppc/hw_disk.c
index 3a82520..54a11f6 100644
--- a/sim/ppc/hw_disk.c
+++ b/sim/ppc/hw_disk.c
@@ -26,10 +26,7 @@
 #include "pk.h"
 
 #include <stdio.h>
-
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 
 #ifndef	SEEK_SET
 #define	SEEK_SET 0
diff --git a/sim/ppc/hw_pal.c b/sim/ppc/hw_pal.c
index 8b07709..f858508 100644
--- a/sim/ppc/hw_pal.c
+++ b/sim/ppc/hw_pal.c
@@ -30,9 +30,7 @@
 #include "cpu.h"
 
 #include <string.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <stdlib.h>
 
 
diff --git a/sim/ppc/main.c b/sim/ppc/main.c
index 83b629e..aa1c85e 100644
--- a/sim/ppc/main.c
+++ b/sim/ppc/main.c
@@ -36,9 +36,7 @@
 #include "sim/sim.h"
 
 #include <stdlib.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <string.h>
 #include <errno.h>
 
diff --git a/sim/ppc/mon.c b/sim/ppc/mon.c
index 4e29ec9..8ab42af 100644
--- a/sim/ppc/mon.c
+++ b/sim/ppc/mon.c
@@ -26,9 +26,7 @@
 #include <stdio.h>
 
 #include <string.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <stdlib.h>
 #ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>
diff --git a/sim/ppc/table.c b/sim/ppc/table.c
index 6399bda..da16967 100644
--- a/sim/ppc/table.c
+++ b/sim/ppc/table.c
@@ -29,9 +29,7 @@
 #include "lf.h"
 #include "table.h"
 
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <stdlib.h>
 
 typedef struct _open_table open_table;
diff --git a/sim/rl78/main.c b/sim/rl78/main.c
index 7c250f7..1eafa33 100644
--- a/sim/rl78/main.c
+++ b/sim/rl78/main.c
@@ -25,9 +25,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <assert.h>
 #include <setjmp.h>
 #include <signal.h>
diff --git a/sim/rx/main.c b/sim/rx/main.c
index e404446..13d0c47 100644
--- a/sim/rx/main.c
+++ b/sim/rx/main.c
@@ -24,9 +24,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <assert.h>
 #include <setjmp.h>
 #include <signal.h>
diff --git a/sim/sh/interp.c b/sim/sh/interp.c
index 5a90cd2..5e0e8c4 100644
--- a/sim/sh/interp.c
+++ b/sim/sh/interp.c
@@ -25,9 +25,7 @@
 #include <stdio.h>
 #include <errno.h>
 #include <signal.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #ifdef HAVE_MMAP
 #include <sys/mman.h>
 # ifndef MAP_FAILED
diff --git a/sim/v850/simops.c b/sim/v850/simops.c
index 69db8aa..326745e 100644
--- a/sim/v850/simops.c
+++ b/sim/v850/simops.c
@@ -12,9 +12,7 @@
 #include <utime.h>
 #endif
 #include <time.h>
-#ifdef HAVE_UNISTD_H
 #include <unistd.h>
-#endif
 #include <stdlib.h>
 #include <string.h>