On Windows, we don't have a notion of ~ meaning "our homedir", so we
were deliberately using an #ifdef to avoid calling expand_filename()
in multiple places. This is silly: The right place to turn a function
into a no-op on a single platform is in the function itself, not in
every single call-site.
This shouldn't be necessary, but apparently the Android cross-compiler
doesn't respect -I as well as it should. (-I is supposed to add to the
*front* of the search path. Android's gcc wrapper apparently likes to add to
the end. This is broken, but we need to work around it.)
