[libcxx-commits] [libcxxabi] Reapply "[libc++abi] Stop copying headers to the build directory" (PR #115379)

[Louis Dionne via libcxx-commits]

ldionne wrote:

FWIW I think the right solution here is for the multi-stage build to install libc++ / libc++abi headers to a temporary location and use those headers. We'd hit the same issue if we started e.g. generating a header only in the installation tree but not in the build tree.

https://github.com/llvm/llvm-project/pull/115379