Thumb1 is a strict subset of Thumb2 so any Thumb1 code would work in both variants. I do not really care about Thumb mode right now though and even if we supported Thumb mode, Thumb1 should be good enough to implement almost everything. The problem is how do we mark ARM non-Thumb assembly correctly (and it shouldn't break even if a Thumb3 is introduced at some point). But I guess if we make it clear that ```ARM_Thumb``` is set for every Thumb variant we won't need ARM_Thumb1 ARM_Thumb2 for now.
```d
version(ARM_Thumb)
else version(ARM)
```