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)
     	 && !shared && !mno-daz-ftz)
  link crtfastmath.o
else
  Don't link crtfastmath.o

gcc/ChangeLog:

	PR target/55522
	PR target/36821
	* config/i386/gnu-user-common.h (GNU_USER_TARGET_MATHFILE_SPEC):
	Link crtfastmath.o whenever -mdaz-ftz is specified. Don't link
	crtfastmath.o when -share or -mno-daz-ftz is specified.
	* config/i386/i386.opt (mdaz-ftz): New option.
	* doc/invoke.texi (x86 options): Document mftz-daz.