/usr/bin/mainDexClasses is in dalvik-exchange 6.0.1+r16-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/../lib/android-sdk/build-tools/23.0.2/mainDexClasses
/usr/bin/../lib/android-sdk/build-tools/23.0.2/mainDexClasses