Retire check for GCC 4.0 under XCode 4.x

XCode 4.x only includes GCC 4.2. Therefore, having `brew doctor` report that
GCC 4.0 is missing only spreads fear, uncertainty and doubt over a situation
that is status quo.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Library/Homebrew/cmd/doctor.rb

@@ -194,6 +194,7 @@ def check_gcc_versions
     EOS
   end
 
+  if MacOS.xcode_version < "4.0"
     if gcc_40 == nil
       puts <<-EOS.undent
         We couldn't detect gcc 4.0.x. Some formulae require this compiler.
@@ -207,6 +208,7 @@ def check_gcc_versions
       EOS
     end
   end
+end
 
 def __check_subdir_access base
   target = HOMEBREW_PREFIX+base