Enum constants are lvalues

[Rob Schluntz]

Enum constants are currently lvalues, making for a cheap conversion to reference. Because of this, & operators are added incorrectly, causing gcc errors.

My first instinct was to say that all enum VariableExprs are non-lvalues, but of course this doesn't work since actual enum variables are lvalues. This will require a more nuanced approach, but I think the basic idea is right.

Example that causes an error:

enum E {
  val
};

int main() {
  E x[3];
  3 ? x[2] : val;
}

[ajbeach]

Fixed a little while ago by checking if the VariableExpr is wrapping a member or not.