Minimal support code for a Cortex-M CPU is added, along with set-up
code for an STM32F4xx MCU, including a UART for a REPL. Tested on
a pyboard. Code size is 77592 bytes.
Unlike bare-arm, which is mostly intended to show raw interpreter size,
without library and support code dependencies. This port is intended to
be a better base to start new ports, and also will include emulation
build to allow debug some aspects of embedded targets on POSIX systems.
This initial commit is verbatim copy of bare-arm code.