Fix workaround for libgmp to work on slack64.

update_script.sh

 	fi
 	# UGLY HACK #3, to upgrade from 13.0 to -current you need
 	# coreutils-8.4 has new dependency for the expr program
-	if [ "$PKG_GMP" != "" -a ! -f "/usr/lib/libgmp.la" ]; then
+	if [ "$PKG_GMP" != "" -a \( ! -f "/usr/lib/libgmp.la" -a ! -f "/usr/lib64/libgmp.la" \) ]; then
 		pkg_install "gmp is not installed. Installing it." $PKG_GMP
 	fi
 	# UGLY HACK #4, to upgrade from 13.1 to 14 you need