[clang] [Clang] Fix visibility macros for c-index-test (PR #171054)

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kkent030315 wrote:

> > Perhaps some of `if (MSVC)` blocks should be changed to `(WIN32 AND NOT MINGW)`.
> 
> `(MSVC OR CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC")` might be better. [gitlab.kitware.com/cmake/cmake/-/issues/19724](https://gitlab.kitware.com/cmake/cmake/-/issues/19724)

I don't think this is suitable for this, let me do some tests. (I did the similar before submitting this PR, didnt worked iirc)

https://github.com/llvm/llvm-project/pull/171054