[flang] [llvm] [OpenMPIRBuilder] Clear the debug location when emitting reduction helpers (PR #211395)

[Spencer Bryngelson via llvm-commits]

sbryngelson wrote:

Closing in favor of #211566, which covers all six reduction helpers rather than the two here, and includes the same barrier fix. Verification is in https://github.com/llvm/llvm-project/pull/211566#issuecomment-5059870726.

https://github.com/llvm/llvm-project/pull/211395