This adds the "volatile" keyword to all the inline assembly. gcc docs say "You can prevent an asm instruction from being deleted by writing the keyword volatile after the asm.". Testing (see comments of github issue #475) shows that indeed gcc can remove some inline asm, in at least this situation:
-multiple calls to cm_is_masked_interrupts() in the same scope/context
- -Os or -O2 optimization
This is problem because the value of PRIMASK could change between two calls to cm_is_masked_interrupts().
Adding the volatile keyword fixes this, and probably costs less than adding a full barrier (like adding "memory" to the clobber list).
While there might be other places that are missing this include, this
particular file is clearly missing them, and has resulted in a few separate bug
reports. Fix it right now, in the name of continuous improvement.
Fixes#310 and #427
