cortex-m3-qemu: a working port
cortex-m3-qemu: refactor the port.

Switch from CodeSourcery to ARM GCC and clean-up some stale files,
also copy `main.c` and `mpconfigport.h` from bare-arm.
qemu-arm: more generic port name.
qemu-arm: update makefile (d553be5).
travis: should test building qemu-arm as well.
Merge pull request #515 from errordeveloper/qemu

Qemu