Toolchain file for building AGL programs

Test:

```
$ export TROUT_TOOLCHAIN_PATH=/path/to/floral/tools/toolchains
$ cd /path_to_android_root/device/google/trout/hal/vehicle/2.0/agl_build/build && cd $_
$ cmake -G "Ninja" -DCMAKE_TOOLCHAIN_FILE=/path_to_android_root/device/google/trout/toolchain/agl_toolchain.cmake ..
$ ninja vehicle_hal_grpc_server
```

Bug: 148877226
Change-Id: I04a1327c4bd2fc27a49ed46491b2f555ca36fa69
1 file changed