This switches the emulator to "single step" emulation mode which is
slower but seems to work-around the current ARMv7 emulation bug.
This allows the dexreopt passes to go through normally.
Allow the dex preoptimization pass for ARMv7 system images to use the
ARMv7-specific kernel image. This is needed to fix the -user builds that
absolutely depend on running the dex preopt in the emulator.
This will hopefully be removed when we'll be able to perform the dex
preopt on the host instead.