gcc: switch back to 4.9

Also sync a tiny difference in docs outputs from gcc-5.
I originally assumed that people will push gcc-5 support to master
long before closure-size gets there, but I overestimated the situation.
We haven't really settled even the issue of ABI switch,
so let's use the same gcc version on closure-size and master.

pkgs/development/compilers/gcc/4.9/default.nix

@@ -215,7 +215,7 @@ stdenv.mkDerivation ({
 
   inherit patches;
 
-  outputs = [ "out" "lib" "doc" ];
+  outputs = [ "out" "lib" "man" "info" ];
   setOutputFlags = false;
   NIX_NO_SELF_RPATH = true;