re PR testsuite/64605 (ERROR: (DejaGnu) proc "libatomic_target_compile lto1738.c lto1738.o object additional_flags=-flto" does not exist.)

	PR testsuite/64605

libatomic/
	* testsuite/lib/libatomic.exp: Do not load gcc-dg.exp.
	* testsuite/libatomic.c/c.exp: Load gcc-dg.exp.

From-SVN: r219722