[automerger skipped] Merge "[DO NOT MERGE] Set RBE_DIR default value to point...

[automerger skipped] Merge "[DO NOT MERGE] Set RBE_DIR default value to point to prebuilts in tree." into qt-dev am: d9cf148d am: 4f66e757 -s ours am: f473b50e -s ours am: 5cc679f1 -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/+/12593960

Change-Id: Ifb5258b9faea6cbc131aecd0aad05fdafb4fc5e7