motivating example:
```nim
iterator p(a: openArray[char]): int =
if a.len != 0:
if a[0] != '/':
discard
for t in p(""): discard
```
The compiler wants to evaluate `a[0]` at compile time even though it is
protected by the if statement above it. Similarly expressions like
`a.len != 0 and a[0] == '/'` have problems. It seems like the logic in
semfold needs to be more aware of branches to positively identify when
it is okay to fail compilation in these scenarios. It's a bit tough
though because it may be the case that non-constant expressions in
branching logic can properly protect some constant expressions.
(cherry picked from commit 850f327713)
While looking at the CI I noticed that there's a couple false positives
for `case` statements that cannot be checked for exhaustiveness since my
changes, this should resolve them.
---------
Co-authored-by: SirOlaf <>
* unnamed break in the block now gives an error
* bootstrap
* fixes
* more fixes
* break with label
* label again
* one moee
* Delete test5.txt
* it now gives a UnnamedBreak warning
* change the URL of bump back to the original one
