Re: top-level configure.ac: factor the libgomp check for posix-like OS

[Gary Funck]

Ended up using the same approach as libatomic,
moving the checking logic into libgupc/configure.tgt.

+# Disable libgupc on unsupported systems.
+if test -d ${srcdir}/libgupc; then
+    if test x$enable_libgupc = x; then
+       AC_MSG_CHECKING([for libgupc support])
+       if (srcdir=${srcdir}/libgupc; \
+               . ${srcdir}/configure.tgt; \
+               test -n "$UNSUPPORTED")
+       then
+           AC_MSG_RESULT([no])
+           noconfigdirs="$noconfigdirs target-libgupc"
+       else
+           AC_MSG_RESULT([yes])
+       fi
+    fi
+fi
+

Thanks,
- Gary