Emil Tsalapatis from Meta reported such a case where 'may_goto 0' insn
is generated by clang compiler. But 'may_goto 0' insn is actually a
no-op so it makes sense to remove that in llvm. The patch is also able
to handle the following code pattern
```
...
may_goto 2
may_goto 1
may_goto 0
...
```
where three may_goto insns can all be removed.
---------
Co-authored-by: Yonghong Song <yonghong.song@linux.dev>
8aae191cb6