We have to use clang from Android NDK to build a library for Android

So none of the newer-compiler-stdenvs nixpkgs offers can help us here.

obelisk/nixpkgs-overlay.nix

 { nix-thunk }: self: super: rec {
   botan2 =
     (super.botan2.override (old: {
-      # Recent versions of Botan depend on fairly new C++ language and library
-      # features which aren't supported by the tools in the default stdenv.
-      # Fortunately, there is a stdenv with a newer version of gcc that does
-      # support those features.  Pick it.
-      stdenv = self.gcc10Stdenv;
-
-      # Also the very old version of OpenSSL available from nixpkgs is marked
-      # as insecure.  Fortunately we don't need SSL from Botan so we can just
+      # The very old version of OpenSSL available from nixpkgs is marked as
+      # insecure.  Fortunately we don't need SSL from Botan so we can just
       # turn this off.  In addition to removing the nixpkgs-visible dependency
       # on OpenSSL, passing null here should cause the expression we're
       # overriding to pass the necessary flags to disable OpenSSL in the build