backend: Allow anything as a match scrutinee

[CohenArthur]

This commit is required for this type of pattern, which isn't really pattern matching:

match something {
    new_binding => { ... }
}

This is required for desugaring for-loops and error propagation expressions.

[philberty]

LGTM with the cmp.rs stuff i am doing i think its going to be time next month to rework the code-gen of math expressions anyway to do if statements potentially instead of switches like we've talked about before