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 bug3;

struct S
{
    int[] arr;
    char[5] ch;
}

class C
{
    int[] arr;
    char[4] crs;
}

void main()
{
    S s;
    s.arr = new int[5];
    s.arr[1] = 32;
    int i;
    i = s.arr[0];
    //assert(s.arr[0] == 0);
    //assert(s.arr[1] == 32);
}