Fix the build when using findleaves.py

This doesn't seem to affect the Kati emulation (at least on Linux), but
findleaves.py on both Mac and Linux checks for duplicate files (via
inode) and only emits build/{target,tools}/Android.mk instead of that
and build/make/{target,tools}/Android.mk.

Bug: 64397960
Test: build/tools/findleaves.py --prune=.git --prune=.repo --dir=.  Android.mk
Test: m -j signapk
Change-Id: Ie6219a809e403e6cc9371b5c0370c7925a592a0d