x86: Add a new option -mdaz-ftz to enable FTZ and DAZ flags in MXCSR.

x86: Add a new option -mdaz-ftz to enable FTZ and DAZ flags in MXCSR.

    if (mdaz-ftz)
      link crtfastmath.o
    else if ((Ofast || ffast-math || funsafe-math-optimizations)
             && !mno-daz-ftz)
      link crtfastmath.o
    else
      Don't link crtfastmath.o

gcc/ChangeLog:

	* config/i386/cygwin.h (ENDFILE_SPEC): Link crtfastmath.o
	whenever -mdaz-ftz is specified. Don't link crtfastmath.o
	when -mno-daz-ftz is specified.
	* config/i386/darwin.h (ENDFILE_SPEC): Ditto.
	* config/i386/gnu-user-common.h
	(GNU_USER_TARGET_MATHFILE_SPEC): Ditto.
	* config/i386/mingw32.h (ENDFILE_SPEC): Ditto.
	* config/i386/i386.opt (mdaz-ftz): New option.
	* doc/invoke.texi (x86 options): Document mftz-daz.