Fixincludes: Handle __FLT_EVAL_METHOD__ == 16 on darwin

The darwin system headers error out on __FLT_EVAL_METHOD__ == 16, which
occurs when the compiler is called with -mavx512fp16 on i386. Allow this
value to proceed past the check (nothing else depends on it in the
system headers).

fixincludes/ChangeLog:

	* inclhack.def: Add new fix on darwin.
	* fixincl.x: Regenerate.
	* tests/base/math.h: Regenerate.