[Aarch64] Customer lowering of COPYSIGN to SIMD should check for NEON availability

For the following test case, clang is crashing for ARM64 architecture
$ cat crash.c
double crash(double a, double b)
{
	return __builtin_copysign(a, b);
}

$ clang -O2 -march=armv8-a+nosimd --target=arm64 -S crash.c -o /dev/null
fatal error: error in backend: Cannot select: 0x7fae361bb4e8: v2i64 = AArch64ISD::BIT 0x7fae361bb210, 0x7fae361bb278, 0x7fae361bb480
Fix: PR51806

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D116581