Array Equals gets lowered to __equals(), but CTFE should not rely on it.
This change to expressionsem.d demonstrates it:
---
// lower some array comparisons to object.__equals(e1, e2)
if (sc.needsCodegen() && <== add this test
(needsArrayLowering || (t1.ty == Tarray && t2.ty == Tarray)))
{
//printf("Lowering to __equals %s %s\n", exp.e1.toChars(), exp.e2.toChars());
---
resulting in:
fail_compilation/diag7420.d(22): called from here: `__equals(y, "abc")`