AstGen: while loop continue expr captures in scope
AstGen: while loop continue expr captures in scope

Before this, the continue expression of a while loop did not have the
capture variable in it, making it incorrectly emit a compile error for
not using the capture, even if it was referenced.

zig-lang/zig,zig-lang/zig,zig-lang/zig,andrewrk/zig,andrewrk/zig