[PATCH] configure: use OBJDUMP determined by libtool [PR95648]

$ac_cv_prog_OBJDUMP contains the --host OBJDUMP that
libtool has inferred. Current config/gcc-plugin.m4 does
not respect the user's choice for OBJDUMP.

	PR plugins/95648
config/

	* gcc-plugin.m4: Use libtool's $ac_cv_prog_OBJDUMP.

gcc/

	* configure: Regenerate.

libcc1/

	* configure: Regenerate.