[clang] [clang] [unittest] Add a test for Generic_GCC::GCCVersion::Parse (PR #69078)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

> I hope that we do not drop `LLVM_LIBRARY_VISIBILITY` arbitrarily from `clang::driver::toolchains::*` classes, just because some unittests need to reference the symbols in a shared object.

That’s a reasonable point.

> ```c
> #if !defined(LLVM_BUILD_SHARED_LIBS)
> ```
> 
> is not great but is not too bad. `-DBUILD_SHARED_LIBS=on` modes are slow to execute tests and are not used often for Release builds.

I guess that’s a reasonable tradeoff. We’d need to do the same for dylib mode as well, which probably is used a bit more. But the main point is that whoever is working on modifying that implementation can run the tests fairly easy, and that they get run somewhere in some configurations at least.

https://github.com/llvm/llvm-project/pull/69078