Move SNAN_TESTS_* out of math-tests.h.

Continuing moving macros out of math-tests.h to smaller headers
following typo-proof conventions instead of using #ifndef, this patch
moves the SNAN_TESTS_* macros for individual types out to their own
sysdeps header (while the type-generic SNAN_TESTS wrapper for those
macros remains in math-tests.h).

Tested for x86_64 and x86, and with build-many-glibcs.py.

	* sysdeps/generic/math-tests-snan.h: New file.
	* sysdeps/generic/math-tests.h: Include <math-tests-snan.h>.
	(SNAN_TESTS_float): Do not define here.
	(SNAN_TESTS_double): Likewise.
	(SNAN_TESTS_long_double): Likewise.
	(SNAN_TESTS_float128): Likewise.
	* sysdeps/i386/fpu/math-tests-snan.h: New file.
	* sysdeps/i386/fpu/math-tests.h: Remove file.
	* sysdeps/ia64/math-tests-snan.h: New file.
	* sysdeps/ia64/math-tests.h: Remove file.
	* sysdeps/x86/math-tests.h: Likewise.
	* sysdeps/x86_64/fpu/math-tests-snan.h: New file.