Hurd: do not include defs.h when compiling MiG stubs since they are compiled as C files

Otherwise, GDB will fail to compile for Hurd.

Approved-By: Tom Tromey <tom@tromey.com>
diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 5295075..2bd1749 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -603,11 +603,12 @@
 # your system doesn't have fcntl.h in /usr/include (which is where it
 # should be according to Posix).
 DEFS = @DEFS@
+GDB_INCLUDED_HEADER = -include $(srcdir)/defs.h
 GDB_CFLAGS = \
 	-I. \
 	-I$(srcdir) \
 	-I$(srcdir)/config \
-	-include $(srcdir)/defs.h \
+	$(GDB_INCLUDED_HEADER) \
 	-DLOCALEDIR="\"$(localedir)\"" \
 	$(DEFS)
 
diff --git a/gdb/config/i386/i386gnu.mn b/gdb/config/i386/i386gnu.mn
index b7414e3..24c58b0 100644
--- a/gdb/config/i386/i386gnu.mn
+++ b/gdb/config/i386/i386gnu.mn
@@ -21,7 +21,9 @@
 	| $(MIGCOM) -sheader /dev/null -server /dev/null -user $*_U.c -header $*_U.h
 
 # MIG stubs are not yet ready for C++ compilation.
-%_S.o %_U.o : COMPILE.post += -x c -include gnu-nat-mig.h
+%_S.o %_U.o : COMPILE.post += -x c
+# Do not include defs.h since it requires C++. Rather include our own gnu-nat-mig.h
+%_S.o %_U.o : GDB_INCLUDED_HEADER = -include gnu-nat-mig.h
 
 NAT_GENERATED_FILES = notify_S.h notify_S.c \
 	process_reply_S.h process_reply_S.c \