kotatogram-desktop: use clang*Stdenv instead of llvmPackages_*.*stdenv

pkgs/top-level/all-packages.nix

@@ -27082,13 +27082,13 @@ with pkgs;
 
     # C++20 is required, darwin has Clang 7 by default, aarch64 has gcc 9 by default
     stdenv = if stdenv.isDarwin
-      then llvmPackages_12.libcxxStdenv
+      then clang12Stdenv
       else if stdenv.isAarch64 then gcc10Stdenv else stdenv;
 
     # tdesktop has random crashes when jemalloc is built with gcc.
     # Apparently, it triggers some bug due to usage of gcc's builtin
     # functions like __builtin_ffsl by jemalloc when it's built with gcc.
-    jemalloc = (jemalloc.override { stdenv = llvmPackages.stdenv; }).overrideAttrs(_: {
+    jemalloc = (jemalloc.override { stdenv = clangStdenv; }).overrideAttrs(_: {
       # no idea how to fix the tests :(
       doCheck = false;
     });