Mangle all included files in the UnpackedTarball directory in
the generated dependency files to point to the target of the
UnpackedTarball instead.  This will cause all files that include them to
be rebuilt on every unpack, which is sound and much easier to maintain
than manually enumerating all internal header files somewhere.

Change-Id: Iaaa9b27450549d26b40d32ae0f740c2d5ef0edc5