[llvm] [JITLink][AArch32] Add explicit visibility macros to functions needed by unittests (PR #116557)

[Lang Hames via llvm-commits]

lhames wrote:

@compnerd Couldn't we have one global `LLVM_TEST_ABI` macro? I think it's fine to claim that we're either building `llvm-project` (all libraries) for testing or we're not.

I wouldn't want these symbols leaking into the ABI of release builds.

https://github.com/llvm/llvm-project/pull/116557