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

[Petr Hosek via libcxx-commits]

petrhosek wrote:

This change broke an existing invariant that the build tree is usable as a toolchain without needing to run an `install` step because the `include` directory no longer contains libc++abi headers after this change.

We rely on that assumptions in multi-stage builds where stage N+1 is using toolchain from stage N (without running the `install` step on stage N), but after this change the stage N output is no longer usable. On the Fuchsia side, this broke all our multi-stage builders.

Can we please revert this change? We'll need to find a different solution for https://github.com/llvm/llvm-project/pull/115077 that doesn't break the existing invariant.

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