Bug 818246 - Part 3: Build system support for XPIDLSRCS in moz.build; r=glandium
Bug 818246 - Part 4: Move XPIDLSRCS into moz.build (auto); rs=glandium

This is the result of running
|mach mozbuild-migrate --list XPIDLSRCS SDK_XPIDLSRCS XPIDL_SOURCES| and
reverting xpcom/sample/*.
Bug 818246 - Part 5: Move XPIDLSRCS into moz.build (manual); r=glandium