c: Fix ICE related to tags and hardbool attribute [PR123856]

The hardbool attribute creates special enumeration types,
but the tag is not set correctly, which causes broken diagnostics
and an ICE with the new helper function to get the tag.

	PR c/123856

gcc/c-family/ChangeLog:
	* c-attribs.cc (handle_hardbool_attribute): Fix TYPE_NAME.

gcc/testsuite/ChangeLog:
	* gcc.dg/pr123856.c: New test.