Update aeabi_divmod.c

On behalf of Herve Sibert (hsibert)
    Corrected division_qr to work on unsigned ints, and simplified
    uint_div_qr accordingly
    Note - this file is no longer ARM-specific.

It fixes #2 (GitHub issue)
Add THREAD_FLAGS_EXIT_ON_IRQ for preempted threads

Adds a THREAD_FLAGS_EXIT_ON_IRQ flag to the saved state of a thread
to make it possible to check that no other thread may resume if there's
a thread preempted by an IRQ.
Fix warning in sta_helloworld

* Fixes a couple of printf warnings visible on higher log levels.
* Cleans up core/arch/arm32/sta/sub.mk
* Adds a compiler.h to provide the __unused macro to avoid warnings
  about unused parameters.