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

[Louis Dionne via cfe-commits]

ldionne wrote:

I had to fix how we were excluding targets from `EXCLUDE_FROM_ALL`, which didn't work as intended and was breaking the MinGW CI. I'll merge this if the CI passes.

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