[libcxx-commits] [libcxx] Reapply "[libc++][C++03] Copy the LLVM 19 headers (#108999)" (PR #112127)

[Louis Dionne via libcxx-commits]

ldionne wrote:

> This PR caused CI failures from `headers_in_modulemap.sh.py`. Can we just exclude the `__cxx03` subdirectory from `is_in_modulemap`?

https://github.com/llvm/llvm-project/pull/113572

https://github.com/llvm/llvm-project/pull/112127