Don't assume ordering of $(wildcard ...)

There are no guarantees on the order of the results from a call to the
wildcard function. In fact, the order usually changes between make 3.81
and make 4.0 (and kati).

Instead, sort the results of wildcard in each sepolicy directory, so
that directory order is preserved, but content ordering is reliable.

Change-Id: I1620f89bbdd2b2902f2e0c40526e893ccf5f7775