Add target-specific dag combines for FAND(x,0) and FOR(x,0). This allows

Add target-specific dag combines for FAND(x,0) and FOR(x,0).  This allows
us to compile:

double test(double X) {
  return copysign(0.0, X);
}

into:

_test:
	andpd	LCPI1_0(%rip), %xmm0
	ret

instead of:
_test:
	pxor	%xmm1, %xmm1
	andpd	LCPI1_0(%rip), %xmm1
	movapd	%xmm0, %xmm2
	andpd	LCPI1_1(%rip), %xmm2
	movapd	%xmm1, %xmm0
	orpd	%xmm2, %xmm0
	ret

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46344 91177308-0d34-0410-b5e6-96231b3b80d8