Don't use this instruction unless you know what you're doing. It does
*not* touch the if/call stacks, so the following code will behave in an
unexpected way (and cannot be fixed by inserting nops):
```
ifu true
for ...
ifu true
break
.end
.end
.else
; will be executed since the inner if is still on the stack
.end
```
breakc has the same problem but does not require a separate condition.
