[dmd-internals] A couple more critical wrong-code bugs

[Don Clugston]

// Ancient and probably the simplest situation that generates wrong
code right now:

1899 AA of fixed-length arrays fails to initialize

// D1 only: This was previously fixed on D2, I've added another small
patch to make it work on D1 as well:

4389 ICE(constfold.c, expression.c), or wrong code: string~=dchar in CTFE

// And a simple ICE:

5248 CTFE Segfault when calling a function on an enum struct