Recommit ENV changes

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
+    @compiler = :gcc_4_0
   end
   alias_method :gcc_4_0, :gcc_4_0_1
 
@@ -131,7 +131,7 @@ module Stdenv
     self.cc  = MacOS.locate("gcc-4.2")
     self.cxx = MacOS.locate("g++-4.2")
 
-    unless cc
+    if cc.empty?
       self.cc  = "#{HOMEBREW_PREFIX}/bin/gcc-4.2"
       self.cxx = "#{HOMEBREW_PREFIX}/bin/g++-4.2"
       raise "GCC could not be found" unless File.exist? cc

Library/Homebrew/os/mac.rb

@@ -99,11 +99,12 @@ module OS
 
     def default_cc
       cc = locate 'cc'
-      Pathname.new(cc).realpath.basename.to_s rescue nil
+      cc.realpath.basename.to_s rescue nil
     end
 
     def default_compiler
       case default_cc
+        when /^gcc-4.0/ then :gcc_4_0
         when /^gcc/ then :gcc
         when /^llvm/ then :llvm
         when "clang" then :clang