[Clang] VectorExprEvaluator::VisitCallExpr / InterpretBuiltin - allow AVX512 VPMULTISHIFTQB intrinsics to be used in constexpr

[RKSimon]

Similar to #161337 - this will require thorough testing to ensure it matches what actual AVX512 hardware does.

__m128i _mm_mask_multishift_epi64_epi8 (__m128i src, __mmask16 k, __m128i a, __m128i b)
__m128i _mm_maskz_multishift_epi64_epi8 (__mmask16 k, __m128i a, __m128i b)
__m128i _mm_multishift_epi64_epi8 (__m128i a, __m128i b)

__m256i _mm256_mask_multishift_epi64_epi8 (__m256i src, __mmask32 k, __m256i a, __m256i b)
__m256i _mm256_maskz_multishift_epi64_epi8 (__mmask32 k, __m256i a, __m256i b)
__m256i _mm256_multishift_epi64_epi8 (__m256i a, __m256i b)

__m512i _mm512_mask_multishift_epi64_epi8 (__m512i src, __mmask64 k, __m512i a, __m512i b)
__m512i _mm512_maskz_multishift_epi64_epi8 (__mmask64 k, __m512i a, __m512i b)
__m512i _mm512_multishift_epi64_epi8 (__m512i a, __m512i b)

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. Check that no other contributor is working on this issue. If someone is assigned to the issue or claimed to be working on it, ping the person. After one week without a response, the assignee may be changed.
2. Leave a comment indicating that you are working on the issue, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Simon Pilgrim (RKSimon)

Similar to #161337 - this will require thorough testing to ensure it matches what actual AVX512 hardware does. ``` __m128i _mm_mask_multishift_epi64_epi8 (__m128i src, __mmask16 k, __m128i a, __m128i b) __m128i _mm_maskz_multishift_epi64_epi8 (__mmask16 k, __m128i a, __m128i b) __m128i _mm_multishift_epi64_epi8 (__m128i a, __m128i b)

__m256i _mm256_mask_multishift_epi64_epi8 (__m256i src, __mmask32 k, __m256i a, __m256i b)
__m256i _mm256_maskz_multishift_epi64_epi8 (__mmask32 k, __m256i a, __m256i b)
__m256i _mm256_multishift_epi64_epi8 (__m256i a, __m256i b)

__m512i _mm512_mask_multishift_epi64_epi8 (__m512i src, __mmask64 k, __m512i a, __m512i b)
__m512i _mm512_maskz_multishift_epi64_epi8 (__mmask64 k, __m512i a, __m512i b)
__m512i _mm512_multishift_epi64_epi8 (__m512i a, __m512i b)

</details>

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Simon Pilgrim (RKSimon)

Similar to #161337 - this will require thorough testing to ensure it matches what actual AVX512 hardware does. ``` __m128i _mm_mask_multishift_epi64_epi8 (__m128i src, __mmask16 k, __m128i a, __m128i b) __m128i _mm_maskz_multishift_epi64_epi8 (__mmask16 k, __m128i a, __m128i b) __m128i _mm_multishift_epi64_epi8 (__m128i a, __m128i b)

__m256i _mm256_mask_multishift_epi64_epi8 (__m256i src, __mmask32 k, __m256i a, __m256i b)
__m256i _mm256_maskz_multishift_epi64_epi8 (__mmask32 k, __m256i a, __m256i b)
__m256i _mm256_multishift_epi64_epi8 (__m256i a, __m256i b)

__m512i _mm512_mask_multishift_epi64_epi8 (__m512i src, __mmask64 k, __m512i a, __m512i b)
__m512i _mm512_maskz_multishift_epi64_epi8 (__mmask64 k, __m512i a, __m512i b)
__m512i _mm512_multishift_epi64_epi8 (__m512i a, __m512i b)

</details>

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

Similar to #161337 - this will require thorough testing to ensure it matches what actual AVX512 hardware does. ``` __m128i _mm_mask_multishift_epi64_epi8 (__m128i src, __mmask16 k, __m128i a, __m128i b) __m128i _mm_maskz_multishift_epi64_epi8 (__mmask16 k, __m128i a, __m128i b) __m128i _mm_multishift_epi64_epi8 (__m128i a, __m128i b)

__m256i _mm256_mask_multishift_epi64_epi8 (__m256i src, __mmask32 k, __m256i a, __m256i b)
__m256i _mm256_maskz_multishift_epi64_epi8 (__mmask32 k, __m256i a, __m256i b)
__m256i _mm256_multishift_epi64_epi8 (__m256i a, __m256i b)

__m512i _mm512_mask_multishift_epi64_epi8 (__m512i src, __mmask64 k, __m512i a, __m512i b)
__m512i _mm512_maskz_multishift_epi64_epi8 (__mmask64 k, __m512i a, __m512i b)
__m512i _mm512_multishift_epi64_epi8 (__m512i a, __m512i b)

</details>

[chaitanyav]

@RKSimon can i work on this?