[clang] [Clang][X86] allow VPERMILPD/S imm intrinsics to be used in constexpr (PR #168044)

[Simon Pilgrim via cfe-commits]

https://github.com/RKSimon requested changes to this pull request.

test cases - again, _mm_permute_ps etc. can be adapted from existing _mm_shuffle_epi32 sse2/avx2/mask/maskz TEST_CONSTEXPR tests, but _mm_permute_pd etc will need fresh tests

https://github.com/llvm/llvm-project/pull/168044