[llvm] [LLVM-C] Upstream `LLVMGetOrInsertFunction` from rustc (PR #162235)

[Nikita Popov via llvm-commits]

nikic wrote:

> As I'm not very familiar with the llvm-c codebase I'm not sure where to add tests for the new function. Any help or directions would be appreciated :)

Either llvm/tools/llvm-c-test or llvm/unittests/IR/FunctionTest.cpp would work. Probably the latter in this case (see the last test function there).


https://github.com/llvm/llvm-project/pull/162235