This is a follow-on task to http://www.google-melange.com/gci/task/view/google/gci2012/7984228

Instead of having environment variables get appended to the beginning or middle of a flags list, make them get added to the end.  It's often a case when compiling that you need to override a flag or path getting set, so we need the ability to both prepend and affix flags to the end of a compilation/linker line.

Provide a patch and output log showing it works.