[automerger skipped] Merge "Set RBE_DIR default value to point to prebuilts in...

[automerger skipped] Merge "Set RBE_DIR default value to point to prebuilts in tree." into rvc-dev am: 461c0d46 am: 772906db am: 5142cae7 -s ours

am skip reason: Change-Id I3392a0f7ac6de818d0c5ba2e113fcb035c6fa0ae with SHA-1 8f8d1126 is in history

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

Change-Id: Ia44163d5152dd4c38c61c4b10ffa15f2c0c96839