strip ccache from CC and CXX from rbconfig.rb

--- ruby-2.0.0-p353/tool/mkconfig.rb~	2013-03-24 17:42:06.000000000 +0200
+++ ruby-2.0.0-p353/tool/mkconfig.rb	2014-03-18 10:34:08.489251715 +0200
@@ -77,6 +77,7 @@
     when /^(?:MAJOR|MINOR|TEENY)$/; next
     when /^RUBY_INSTALL_NAME$/; next if $install_name
     when /^RUBY_SO_NAME$/; next if $so_name
+    when /^(CC|CXX)$/; val.sub!(/ccache /, '')
     when /^arch$/; if val.empty? then val = arch else arch = val end
     when /^sitearch$/; val = '$(arch)' if val.empty?
     end