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

[Louis Dionne via cfe-commits]

ldionne wrote:

CC @petrhosek @vitalybuka since this broke your setups last time. The reproduction steps were really non-trivial so I never got around to reproducing, but it would be great to see if this is still problematic.

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