Add auto build script

1. Build clang compiler from scratch.
2. Use custom clang compiler to build master branch.
3. Test master build with all connected devices.

Test: test `python ./test_compiler` for local AOSP master branch with
angler and bullhead connected.
Bug:62292583

Change-Id: Ic1d1f4b969f363d42ff5ec25ae0f23d10345fe76