osl: fix build on darwin

(cherry picked from commit 12b56aea48)

pkgs/top-level/all-packages.nix

@@ -11765,7 +11765,10 @@ with pkgs;
   osl = libsForQt5.callPackage ../development/compilers/osl {
     boost = boost179;
     libclang = llvmPackages_15.libclang;
-    clang = clang_15;
+    clang =
+      if stdenv.cc.libcxx != null
+      then (overrideLibcxx llvmPackages_15.stdenv).cc
+      else clang_15;
     llvm = llvm_15;
   };