[llvm] [mlir] [OMPIRBuilder][OpenMP][LLVM] Modify and use ReplaceConstant utility in convertTarget (PR #94541)

[via llvm-commits]

agozillon wrote:

> LGTM

Thank you very much! I'll pester one other reviewer for a review/sign-off and then hopefully it'll be good to land. 

https://github.com/llvm/llvm-project/pull/94541