[automerger skipped] Merge "Set RBE_DIR default value to point to prebuilts in tree." into rvc-dev am: 461c0d46 -s ours

am skip reason: Change-Id I3392a0f7ac6de818d0c5ba2e113fcb035c6fa0ae with SHA-1 ba6d777f is in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/build/+/12445424

Change-Id: I54ceb29a67ff50c7335dd284cb1841b0697bdf9f