[libcxx] [libcxxabi] [libunwind] [runtimes] Always define cxx_shared, cxx_static & other targets (PR #80007)

[Paul Kirth via cfe-commits]

ilovepi wrote:

I think I understand what's happening, but not why. We don't normally build `cxx_shared` on Linux, but now we do. I'm not sure why that's causing a problem on this test per se, but we set `LIBCXX_ENABLE_SHARED=OFF` in our build files, so I'm surprised its happening now. In fact under `build/runtimes/runtimes-x86_64-unknown-linux-gnu-bins` I only see `LIBCXX_ENABLE_SHARED=OFF` in all of the CMake files. Seems like this isn't propagating correctly anymore?

https://github.com/llvm/llvm-project/pull/80007