Bug 1063860 - Refresh some of the variable/tier associations in mozbuild.context. r=gps
Bug 1059255 - Stop building stdc++compat as a real library. r=mshal

Incidentally, this makes the build fail because stdc++compat.o then appears
twice on the libxul linkage command line. This, in turn, is because
widget/xremoteclient creates both a program and an intermediate library for
libxul. The Program() template adds stdc++compat to the directory data,
which ends up being added to libxul as well. The same kind of issue arises
when linking the gtest-enabled libxul.

While eventually we'll be able to avoid those problems, it's not the case
yet, so work around the issue by making expand-libs skip .desc files that
appear multiple times.
Bug 1059255 - Make stdc++compat errors fatal. r=mshal
Bug 1051209 - Properly link libxul.so on GTK+3 builds after bug 1045783. r=mshal