[clang] [llvm] [Clang][OpenMP] Move declare simd codegen into OMPIRBuilder (PR #186030)

[Kiran Chandramohan via cfe-commits]

kiranchandramohan wrote:

Thanks for this refactoring. Do we have existing tests for the following?
	1.	x86 masked vs. unmasked emission, and
	2.	AArch64 NEON vs. SVE, including a case with explicit simdlen.

https://github.com/llvm/llvm-project/pull/186030