Add support for using a homebrew-compiled gcc 4.8 to compile other formulas.

gistfile1.diff

diff --git a/Library/Homebrew/extend/ENV.rb b/Library/Homebrew/extend/ENV.rb
index 8d971eb..47ae246 100644
--- a/Library/Homebrew/extend/ENV.rb
+++ b/Library/Homebrew/extend/ENV.rb
@@ -164,6 +164,16 @@ module HomebrewEnvExtension
   end
   alias_method :gcc_4_2, :gcc
 
+  def gcc48
+    self['CC'] = self['OBJC'] = "#{HOMEBREW_PREFIX}/bin/gcc-4.8"
+    self['CXX'] = self['OBJCXX'] = "#{HOMEBREW_PREFIX}/bin/g++-4.8"
+    raise "GCC could not be found" unless File.exist? self['CC']
+
+    replace_in_cflags '-O4', '-O3'
+    set_cpu_cflags
+    @compiler = :gcc48
+  end
+
   def llvm
     self['CC'] = self['OBJC'] = MacOS.locate("llvm-gcc")
     self['CXX'] = self['OBJCXX'] = MacOS.locate("llvm-g++")
@@ -351,6 +361,8 @@ module HomebrewEnvExtension
       :llvm
     elsif ARGV.include? '--use-clang'
       :clang
+    elsif ARGV.include? '--use-gcc48'
+      :gcc48
     elsif self['HOMEBREW_USE_CLANG']
       :clang
     elsif self['HOMEBREW_USE_LLVM']