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)

module typeinfo2;

void main()
{
    auto ti = typeid(float);
    float f = 2.5;
    hash_t fh = ti.getHash(&f);
    assert(ti.next is null);
    float g = 4.0;
    ti.swap(&f,&g);
    assert(f == 4.0 && g == 2.5);
    assert(fh == *cast(uint*)(&g));
    assert(!ti.flags);
}