Test case:
---
void foo(const int x) {
   int delegate(int t) bar = (int t){ return x; };
}
------
bug.d(3): Error: cannot implicitly convert expression (__dgliteral1) of type c
onst(int) delegate(int t) to int delegate(int t)
----
// But this one works....
void foo(const int x) {
   int delegate(int t) bar = (int t){ return x+0; };
}

I think the reason for this is that 
TypeDelegate::implicitConvTo() is not defined.
It should allow implicit conversions of return value between type const(T), immutable(T), and type T, when T is a value type. Certainly for delegate literals.