[automerger skipped] [DO NOT MERGE] Add RBE support for Javac, R8, and D8 if respective env vars are set. am: c9a030aa am: 5507116c -s ours am: 33466e38 -s ours am: 5af3f2f5 -s ours am: 93083cfc -s ours

am skip reason: Change-Id I252ff5dd8e372edf8c86e25348c8a2bfab41d70d with SHA-1 a9cc25d7 is in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/build/+/12468474

Change-Id: I9debab09392754e546de5bca20bc72fb38e28ab6