ttype assertion resolution is too strict

[Rob Schluntz]

Assertions on ttype variables are currently too strict with regards to qualifiers.

forall(ttype T | { void foo(T); }) void bar(T x);
void foo(int);

int main() {
  const int x;
  bar(x);
}

T binds to [int], and there is no void foo(const int) in scope. Notably, using dtype instead of ttype works in the above example, so it is not a general assertion inference problem.

Adding void foo(const int); or casting (int)x are temporary workarounds.

[Rob Schluntz <rschlunt@…>]

In 1dcd52a3:

Disregard outermost const, volatile, _Atomic qualifiers on parameters when unifying function types [fixes #48]