Fix breakage: bad path join using '/' literal am: 2a5c090c am: cf96d25b am: ec84245e

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/2052015



Change-Id: I5e8ea66626e0cde29a7c24f370b85548ae6b5d4a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>