stage2: implementation of `@setEvalBranchQuota`:

`@setEvalBranchQuota` can be called before the comptime/inline call
stack is created.

For example:

```zig
@setEvalBranchQuota(100);
comptime {
    while (true) {}
}
```

Here we need to set the branch_quota before the comptime block creates a
scope for the branch_count.
638f93ebdcg-w1 committed on 1/4/2021, 7:42:52 PM· committed by Andrew Kelleyparentaa0906e
5 files changedLine totals unavailable