llvmPackages_15.libcxx: fix the generated linker script

See:
 - #214524 (comment)
 - llvm/llvm-project@57c7bb3
 - https://reviews.llvm.org/D133566

We can drop this patch in `llvmPackages_16`.

Fixes #214524.

pkgs/development/compilers/llvm/15/libcxx/default.nix

@@ -1,5 +1,5 @@
 { lib, stdenv, llvm_meta
-, monorepoSrc, runCommand
+, monorepoSrc, runCommand, fetchpatch
 , cmake, ninja, python3, fixDarwinDylibNames, version
 , cxxabi ? if stdenv.hostPlatform.isFreeBSD then libcxxrt else libcxxabi
 , libcxxabi, libcxxrt, libunwind
@@ -47,6 +47,15 @@ stdenv.mkDerivation rec {
 
   patches = [
     ./gnu-install-dirs.patch
+    # See:
+    #   - https://reviews.llvm.org/D133566
+    #   - https://github.com/NixOS/nixpkgs/issues/214524#issuecomment-1429146432
+    # !!! Drop in LLVM 16+
+    (fetchpatch {
+      url = "https://github.com/llvm/llvm-project/commit/57c7bb3ec89565c68f858d316504668f9d214d59.patch";
+      hash = "sha256-AaM9A6tQ4YAw7uDqCIV4VaiUyLZv+unwcOqbakwW9/k=";
+      relative = "libcxx";
+    })
   ] ++ lib.optionals stdenv.hostPlatform.isMusl [
     ../../libcxx-0001-musl-hacks.patch
   ];

pkgs/test/default.nix

@@ -59,7 +59,6 @@ with pkgs;
 
             # libcxxStdenv broken
             # fix in https://github.com/NixOS/nixpkgs/pull/216273
-            (filter (n: n != "llvmPackages_15"))
           ] ++ lib.optionals (stdenv.hostPlatform.isLinux && stdenv.hostPlatform.isAarch64) [
             # libcxx does not build for some reason on aarch64-linux
             (filter (n: n != "llvmPackages_7"))