define replacement for enable and disable irq for m0

[gullradriel]

Following the comment here: #1517 (comment)

We are getting undefined reference to enable/disable irq calls.

I'm providing a fix for build on m0, based on the definition that can be found in chibios.

[miek]

Sounds good to me.

I think it would be worth adding the "memory" clobber you mentioned in #1517 though. As far as I can tell from the docs & various discussions online, the compiler can choose to re-order instructions potentially putting the load/store on the wrong side of the asm statement. Adding that clobber argument acts as a memory barrier and prevents that from happening.

[gullradriel]

Thanks, I'm adding it right now.

[gullradriel]

Thanks :-)