gama: fix build on aarch64-darwin

pkgs/applications/science/geometry/gama/default.nix

···
 
   nativeBuildInputs = [ texinfo zip ];
 
+  env.CXXFLAGS = lib.optionalString stdenv.cc.isClang "-include sstream";
+
   nativeCheckInputs = [ octave libxml2 ];
   doCheck = true;