[llvm] [OMPIRBuilder] Prevent dangling InsertPt in IRBuilder. (PR #148887)

[Tom Eccles via llvm-commits]

tblah wrote:

Thanks for fixing this. Is it possible to set no insert point? Like a nullptr. The insert points added here aren't really meaningful to anything that tries to use them.

https://github.com/llvm/llvm-project/pull/148887