[X86] Use separate builtins for fma4 scalar intrinsics. Use negations to remove some...

[X86] Use separate builtins for fma4 scalar intrinsics. Use negations to remove some of the scalar fma3 builtins.

fma4 instructions zero the upper bits of the xmm register. fma3 instructions leave the bits unmodified. This requires separate builtins for the different semantics.

While we're cleaning up the scalar builtins this also removes the fma3 fmsub/fnmadd/fnmsub builtins by using negates in the header file.

llvm-svn: 318985