[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: 0432d28c -s ours am: 0b727747 -s ours am: d94464b9 -s ours

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

Change-Id: Ifff79ed45f907ccecd6c490e8223b5321b2745eb