Implement first D-specific optimization pass: -simplify-drtcalls. It uses the machinery of the standard -simplify-libcalls pass, but optimizes calls to the D runtime instead of calls to C libraries. At the moment, these optimizations are implemented by this pass: - Avoid the runtime call for `arr.length = newlen` if it can determine that the new length isn't longer than the old one. - Ditto for `cast(T[]) arr` if it will clearly always succeed. (e.g. if the length of the original array is zero, or if the old element size is a multiple of the new element size)

struct Color {
  uint c;
  static Color opCall(uint _c) { Color ret; ret.c = _c; return ret; }
}

// run at compile time
static const Color white = Color(0xffffffff);

void main()
{
  assert(white.c == 0xffffffff);
}