Current code does not build on Cortex-M0, seems like it does not like
subs:
Error: instruction not supported in Thumb16 mode -- `subs r3,#1'
Adding a unified assembler language declaration in the snippet seems to
fix the problem, also add an M0+ board so this is tested in CI.
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
87e20308bd