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

[Lang Hames via llvm-commits]

lhames wrote:

@compnerd Can you dllexport and then dllimport the same symbol within a static link? (Apologies for my lack of windows knowledge here). In that case I'm imagining that we could have something as simple as:
```c++
#ifndef NDEBUG
#define LLVM_UNITTEST_EXPORT __declspec(dllexport)
#else
#define LLVM_UNITTEST_EXPORT
#endif

Then wrap the unit test in `#ifndef NDEBUG` and unconditionally dllimport the decl?

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