llvmPackages_15.libcxx: fix the generated linker script
See:
- https://github.com/NixOS/nixpkgs/issues/214524#issuecomment-1429146432
- https://github.com/llvm/llvm-project/commit/57c7bb3ec89565c68f858d316504668f9d214d59
- https://reviews.llvm.org/D133566
We can drop this patch in `llvmPackages_16`.
Fixes #214524.
authored by