Member predicate Function::hasTrailingReturnType

Holds if this function has a trailing return type.

Note that this is true whether or not deduction took place. For example, this holds for both e and f, but not g or h:

auto e() -> int { return 0; }
auto f() -> auto { return 0; }
auto g() { return 0; }
int h() { return 0; }