[clang] [compiler-rt] [libcxx] [llvm] [libc++] Replace LIBCXX_ENABLE_STATIC_ABI_LIBRARY & friends by a new LIBCXX_CXX_ABI choice (PR #112978)

[Louis Dionne via cfe-commits]

ldionne wrote:

> Looking at our current cmake config, we're using:
> 
> ```
> -DLIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY=ON \
> -DLIBCXX_ENABLE_ABI_LINKER_SCRIPT=ON \
> ```
> 
> Do I understand correctly that the new replacement for that would be?
> 
> ```
> -DLIBCXX_ABILIB_FOR_SHARED="shared-libcxxabi" \
> -DLIBCXX_ABILIB_FOR_STATIC="merged-libcxxabi" \
> -DLIBCXX_ENABLE_ABI_LINKER_SCRIPT=ON \
> ```

Yes, that is correct. This patch should be changing your CMake config as well, unless that config is not visible in the monorepo (or if I missed it).

> 
> And those LIBCXX_ABILIB options are also the defaults, if I'm reading the docs right.

Not quite. `LIBCXX_ABILIB_FOR_SHARED="shared-libcxxabi"` is the default for the shared library. However for the static library, the default is `LIBCXX_ABILIB_FOR_STATIC="static-libcxxabi"`. That might not be the most useful default (`merged-libcxxabi` would be more useful IMO), but it's the status quo and this patch doesn't change that.

https://github.com/llvm/llvm-project/pull/112978