development_tools: simplify generic default_compiler logic.

Library/Homebrew/development_tools.rb

@@ -31,12 +31,10 @@ class DevelopmentTools
     end
 
     def default_compiler
-      case default_cc
-      # if GCC 4.2 is installed, e.g. via Tigerbrew, prefer it
-      # over the system's GCC 4.0
-      when /^gcc-4.0/ then gcc_42_build_version ? :gcc : :gcc_4_0
-      when /^gcc/ then :gcc
-      else :clang
+      if default_cc =~ /^gcc/
+        :gcc
+      else
+        :clang
       end
     end