llvmPackages_13.lld: add postPatch to fix Darwin build

pkgs/development/compilers/llvm/13/lld/default.nix

@@ -18,6 +18,14 @@ stdenv.mkDerivation rec {
     ./gnu-install-dirs.patch
   ];
 
+  # On Darwin the llvm-config is perhaps not working fine as the
+  # LLVM_MAIN_SRC_DIR is not getting set correctly, and the build fails as the
+  # include path is not correct.
+  postPatch = lib.optionalString stdenv.isDarwin ''
+    substituteInPlace MachO/CMakeLists.txt --replace \
+      '(''${LLVM_MAIN_SRC_DIR}/' '(../'
+  '';
+
   nativeBuildInputs = [ cmake ];
   buildInputs = [ libllvm libxml2 ];