Support SSE float environment in fenv.h functions.

 	Support SSE float environment in fenv.h functions.

	* cpu_features.c: New file.
	* cpu_features.h: New file.
	* crt1.c: Include "cpu_features.h".
	(__mingw_CRTStartup): Call cpu_features_init().
	* Makefile.in (MING_OBJS): Add cpu_features.c.
	(SRCDIST_FILES): Add cpu_features.c, cpu_features.h.
	* include/fenv,h ( fenv_t;): Append  __mxcsr field.
	(__MXCSR_EXCEPT_FLAG_SHIFT): New define.
	(__MXCSR_EXCEPT_MASK_SHIFT): New define.
	(__MXCSR_ROUND_FLAG_SHIFT): New define.
	* mingwex/feclearexcept.c: Include "cpu_features.h".
	Handle SSE environment.
	* mingwex/fegetenv.c: Likewise.
	* mingwex/feholdexcept.c: Likewise.
	* mingwex/fesetenv.c: Likewise.
	* mingwex/fesetexceptflag.c: Likewise.
	* mingwex/fesetround.c: Likewise.
	* mingwex/fetestexcept.c: Likewise.
	* mingwex/feupdateenv.c: Likewise.
	* mingwex/fegetround.c: Add comment.