libtool.m4: Update hardcode_shlibpath_var for OpenBSD

When generating an executable in OpenBSD, the executable fails to
generate when shlibpath_var, LD_LIBRARY_PATH, is used solely to
locate dependent libraries.

For hardcoding library paths in OpenBSD, see documentation for
hardcode_direct and hardcode_libdir_flag_spec.

* m4/libtool.m4: Update hardcode_shlibpath_var from 'no' to 'unsupported'
  by removing 'with_gnu_ld=no' for OpenBSD.

m4/libtool.m4

diff --git a/m4/libtool.m4 b/m4/libtool.m4
index d0d3686..2955ade 100644
--- a/m4/libtool.m4
+++ b/m4/libtool.m4
@@ -5091,9 +5091,6 @@
     # we just hope/assume this is gcc and not c89 (= MSVC++ or ICC)
     with_gnu_ld=yes
     ;;
-  openbsd*)
-    with_gnu_ld=no
-    ;;
   esac
 
   _LT_TAGVAR(ld_shlibs, $1)=yes