Merge "Add environment variable BUILD_FROM_SOURCE_STUB" into main am:...

Merge "Add environment variable BUILD_FROM_SOURCE_STUB" into main am: 37d679df am: 404bf92c am: 9d4a61d4

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/2831230



Change-Id: Ia9373171a57dbcabf8772e5a37b36d3d070eaafd
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>