Revert header inclusion changes that break math/ testing on x86_64.

	Revert:
	2017-02-16  Zack Weinberg  <zackw@panix.com>

	* sysdeps/x86_64/fpu/math-tests-arch.h: Include cpu-features.h.
	Don't include init-arch.h.
	* sysdeps/x86_64/multiarch/test-multiarch.h: Include cpu-features.h.
	Don't include init-arch.h.