Revert "stdenv: set correct compiler symbol for gcc 4.0"

This reverts commit f4dc5614953b3b90acc28c83262d56587b0616b1.

Library/Homebrew/extend/ENV/std.rb

@@ -119,7 +119,7 @@ module Stdenv
     self.cxx = "#{MacOS.dev_tools_path}/g++-4.0"
     replace_in_cflags '-O4', '-O3'
     set_cpu_cflags '-march=nocona -mssse3'
-    @compiler = :gcc_4_0
+    @compiler = :gcc
   end
   alias_method :gcc_4_0, :gcc_4_0_1