[llvm] [mlir] [llvm][OpenMP] Add implicit cast to omp.atomic.read (PR #114659)

[Michael Kruse via llvm-commits]

Meinersbur wrote:

I added `emitAtomicLoadBuiltin` and `emitAtomicStoreBuiltin` into #101966, and use it within OpenMPIRBuilder. The patch is not ready yet, tests are not updated and code duplication needs to be reduced.

However, I hope the benfits become clear:
 * Just one case instead of multiple depending on data type.
 * All data types (incl. complete) able to use the cmpxchg,load,store,atomicrmw etc instead of the libcall fallback. Only the data size matters, not the type.

https://github.com/llvm/llvm-project/pull/114659