Driver: -ccc-install-dir should affect cc1 -resource-dir

-ccc-install-dir is supposed to cause the compiler to behave as-if it
were installed in the indicated location. It almost does, but misses
anything that's relying on the resource directory (libc++ header search,
in particular). The resource dir is resolved too early, before command
line args are handled.

The fix is simply to move handling of the resource dir until after we
know if a -ccc-install-dir is present.

rdar://13402696