[libcxx-commits] [libcxx] [libcxxabi] [libc++] Fix broken configuration system-libcxxabi on Apple (PR #110920)

[Michał Górny via libcxx-commits]

mgorny wrote:

I think it were:

```
commit ec2e1cae2c6330cd1e3b7f580702f1949827899a
Author:     Louis Dionne <ldionne.2 at gmail.com>
AuthorDate: 2024-10-09 14:46:59 +0200
Commit:     Tobias Hieta <tobias at hieta.se>
CommitDate: 2024-11-18 17:01:02 +0100

    [libc++] Fix broken configuration system-libcxxabi on Apple (#110920)
    
    On Apple platforms, using system-libcxxabi as an ABI library wouldn't
    work because we'd try to re-export symbols from libc++abi that the
    system libc++abi.dylib might not have. Instead, only re-export those
    symbols when we're using the in-tree libc++abi.
    
    This does mean that libc++.dylib won't re-export any libc++abi symbols
    when building against the system libc++abi, which could be fixed in
    various ways. However, the best solution really depends on the intended
    use case, so this patch doesn't try to solve that problem.
    
    As a drive-by, also improve the diagnostic message when the user forgets
    to set the LIBCXX_CXX_ABI_INCLUDE_PATHS variable, which would previously
    lead to a confusing error.
    
    Closes #104672
    
    (cherry picked from commit 21da4e7f51c7adfd0b1c5defc8bd0d16ea1ce759)
```

https://github.com/llvm/llvm-project/pull/110920