Move EXCEPTION_SET_FORCES_TRAP out of math-tests.h.

Completing the move of macros out of math-tests.h to smaller headers
following typo-proof conventions instead of using #ifndef, this patch
moves the EXCEPTION_SET_FORCES_TRAP macro out to its own
math-tests-trap-force.h header.

Tested with build-many-glibcs.py.

	* sysdeps/generic/math-tests-trap-force.h: New file.
	* sysdeps/generic/math-tests.h: Include <math-tests-trap-force.h>.
	(EXCEPTION_SET_FORCES_TRAP): Do not define here.
	* sysdeps/powerpc/math-tests.h: Remove file.
	* sysdeps/powerpc/fpu/math-tests-trap-force.h: New file.