Remove pre-GCC-4.7 conform/ test XFAILs.

Now that GCC 4.7 or later is required to build glibc, this patch
removes three conform/ test XFAILs that related to missing C11 support
in GCC 4.6.

Tested for x86_64 and x86 (conform/ tests).

	* conform/Makefile (test-xfail-ISO11/complex.h/conform): Remove
	variable.
	(test-xfail-ISO11/stdalign.h/conform): Likewise.
	(test-xfail-ISO11/stdnoreturn.h/conform): Likewise.