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

[Thomas Fransham via llvm-commits]

fsfod wrote:

> Thanks for bringing this up. These functions were never meant to be exported publically, we only want to access them for testing. Does that make a difference for the LLVM_ABI tag? Do we have similar situations anywhere else in the codebase?

Because these are not declared in any header there wouldn't really be any expectation that these could be consumed by anything but tests. 
Yes i've had to fix missing exports of internal symbols used by tests in other places of the LLVM codebase, sometimes its been internal headers which are easier to automate annotations.

> In order to avoid confusion, we could also make a local LLVM_TEST_ABI redefinition with with a note

Maybe i could, but previous discussions i've had with @compnerd he wanted to avoid proliferation of lots of different symbol visibility macros. 

>  if this only affects Windows, we could disable the respective unittets there. What do you think?

Its only affects windows atm, but in the future when default symbol visibility is changed changed to hidden for the LLVM shared library these would need the same annotations as windows 

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