libgomp: Use sizeof(void*) based checks instead of looking through $CC $CFLAGS for...

libgomp: Use sizeof(void*) based checks instead of looking through $CC $CFLAGS for -m32/-mx32

Some gcc configurations default to -m32 but support -m64 too.  This patch
just makes the ILP32 tests more reliable by following what e.g. libsanitizer
configury does.

2021-03-04  Jakub Jelinek  <jakub@redhat.com>

	* configure.ac: Add AC_CHECK_SIZEOF([void *]).
	* plugin/configfrag.ac: Check $ac_cv_sizeof_void_p value instead of
	checking of -m32 or -mx32 options on the command line.
	* config.h.in: Regenerated.
	* configure: Regenerated.