[clang] [X86] Allow PSHUFD/PSHUFLW/PSHUFW intrinsics in constexpr. (PR #161210)

[Nagraj Gaonkar via cfe-commits]

NagrajMG wrote:

@RKSimon The test and the builtin def files undergo massive structural change if I run formatter on them?
I need to ignore them right?

https://github.com/llvm/llvm-project/pull/161210