[clang] Revert "[Headers][X86] Allow SSE/AVX/AVX512 unpck intrinsics to be used in constexpr" (PR #153491)

[Jasmine Tang via cfe-commits]

badumbatish wrote:

hi @nikic, i've opened a PR to fix the test failure at https://github.com/llvm/llvm-project/pull/153473, i'm not sure if this should revert or the other PR should go through

https://github.com/llvm/llvm-project/pull/153491