Use x constraints for operands to vfmaddss and vfmaddsd

Use x constraints for operands to vfmaddss and vfmaddsd

While these instructions accept memory operands, only one operand
may be a memory operand.  Giving two operands xm constraints gives
the compiler the option of using memory for both operands, which
would result in invalid assembly code.  Using x for all operands is
more appropriate, as most x86_64 calling conventions will pass the
arguments in registers anyway.

2013-05-15  Peter Collingbourne  <pcc@google.com>

	* sysdeps/x86_64/fpu/multiarch/s_fma.c (__fma_fma4): Replace xm
	constraints with x constraints.
	* sysdeps/x86_64/fpu/multiarch/s_fmaf.c (__fmaf_fma4): Likewise.