Merge changes from topics "extdir", "threadvars" am: d2149e6a81 am: df4ea086a4 am: 8a05c8df34 am: 75d6c5ee4e

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/1988355

Change-Id: I1fdff5d1da2a6684571cddf21a8ad9340681ea49