omp_locks: C Array

[ax3l]

Summary

Use a plain C array over a std::array for omp_locks. Primarily because this causes linker issues on MSVC/Clang-Cl, secondarily because omp_locks might violate in some implementations the type requirements of std::array (MoveConstructible and MoveAssignable type T).
https://en.cppreference.com/w/cpp/container/array

Additional background

Potentially a fix for #3795

Testing in conda-forge/impactx-feedstock#28

Checklist

The proposed changes:

• fix a bug or incorrect behavior in AMReX
• add new capabilities to AMReX
• changes answers in the test suite to more than roundoff level
• are likely to significantly affect the results of downstream AMReX users
• include documentation in the code and/or rst files, if appropriate

[ax3l]

The error now is:

lld-link: error: undefined symbol: __declspec(dllimport) struct omp_lock_t *amrex::OpenMP::omp_locks

[WeiqunZhang]

The types in OMP are likely simple C types. So it should not be an issue for std::array. Even if it is so, it should have failed before the link stage.

In llvm, omp_lock_t is a simple struct with a void*.

https://github.com/llvm/llvm-project/blob/ad8c8281363261929b53b0a519cd20e9e2445343/openmp/runtime/src/include/omp.h.var#L83

Anyway, we can merge this and try to fix it in another way.