[Clang] VectorExprEvaluator::VisitCallExpr / InterpretBuiltin - add MMX/SSE/AVX2 PSIGN intrinsics to be used in constexpr

[RKSimon]

Similar to #152524 - add handling for __builtin_ia32_psignd to VectorExprEvaluator::VisitCallExpr and InterBuiltin.cpp

_mm_sign_pi8  _mm_sign_epi8  _mm256_sign_epi8
_mm_sign_pi16 _mm_sign_epi16 _mm256_sign_epi16
_mm_sign_pi32 _mm_sign_epi32 _mm256_sign_epi32

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Simon Pilgrim (RKSimon)

Similar to #152524 - add handling for __builtin_ia32_psignd to VectorExprEvaluator::VisitCallExpr and InterBuiltin.cpp ``` _mm_sign_pi8 _mm_sign_epi8 _mm256_sign_epi8 _mm_sign_pi16 _mm_sign_epi16 _mm256_sign_epi16 _mm_sign_pi32 _mm_sign_epi32 _mm256_sign_epi32 ```

[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-backend-x86

Author: Simon Pilgrim (RKSimon)

Similar to #152524 - add handling for __builtin_ia32_psignd to VectorExprEvaluator::VisitCallExpr and InterBuiltin.cpp ``` _mm_sign_pi8 _mm_sign_epi8 _mm256_sign_epi8 _mm_sign_pi16 _mm_sign_epi16 _mm256_sign_epi16 _mm_sign_pi32 _mm_sign_epi32 _mm256_sign_epi32 ```

[llvmbot]

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

Author: Simon Pilgrim (RKSimon)

Similar to #152524 - add handling for __builtin_ia32_psignd to VectorExprEvaluator::VisitCallExpr and InterBuiltin.cpp ``` _mm_sign_pi8 _mm_sign_epi8 _mm256_sign_epi8 _mm_sign_pi16 _mm_sign_epi16 _mm256_sign_epi16 _mm_sign_pi32 _mm_sign_epi32 _mm256_sign_epi32 ```

[ybc1356]

Hi, I am looking to get started on contributing to llvm and would want to work on this issue.