Evidently on Windows, the newfangled ucpp handles #include "foo"
differently from #include <foo> and treats it as a relative path, while
the angle brackets always result in absolute paths.
Since relative paths result in infinite rebuilds if make is invoked in a
different directory, don't use #include "foo" in IDL files.

Change-Id: Iedcda3a4be5542389a0be086f14541cda8dc5323