qgit: Compile with -O3. This brings a significant speedup in C++ code.

I wonder what optimization flags qt is compiled with.

svn path=/nixpkgs/trunk/; revision=12300

pkgs/applications/version-management/qgit/default.nix

@@ -14,4 +14,5 @@ stdenv.mkDerivation rec {
     sha256 = "0qmgd1cjny5aciljpvn2bczgdvlpgd2f7wzafda24zj4mzqnppsq";
   };
   buildInputs = [qt libXext libX11];
+  configureFlags = "CXXFLAGS=-O3";
 }