Bug 864774 - Part 1: Support CPP_SOURCES in moz.build; r=gps

From 634fb39c43c258feca8c814c450cd9dfe30a8353 Mon Sep 17 00:00:00 2001
Bug 864774 - Part 2: Move CPPSRCS to moz.build as CPP_SOURCES; r=joey CLOSED TREE

From 9e0ba7f425143f545eb6c4b26a9a96b5ade4d8e9 Mon Sep 17 00:00:00 2001