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.

config/
	* gcc-plugin.m4: Use libtool's $ac_cv_prog_OBJDUMP.
1 file changed