message: overdrawanalyzer: Simplify depth code
  Instead of selecting a Z or reverse Z value in the inner loop, adjust
  the logic outside of the loop so that it naturally comes out flipped.
diff: @@ -55,9 +55,15 @@ namespace
  // flip backfacing triangles to simplify rasterization logic
  if (sign)
  {
  + // flipping v2 & v3 preserves depth gradients since they're based on v1
  std::swap(v2x, v3x);
  std::swap(v2y, v3y);
  std::swap(v2z, v3z);
  +
  + // flip depth since we rasterize backfacing triangles to second buffer with reverse Z; only v1z is used below
  + v1z = kViewport - v1z;
  + DZx = -DZx;
  + DZy = -DZy;
  }
  // coordinates, 28.4 fixed point
  @@ -107,11 +113,9 @@ namespace
  // check if all CXn are non-negative
  if ((CX1 | CX2 | CX3) >= 0)
  {
  - float z = sign ? kViewport - ZX : ZX;
  -
  - if (z >= buffer->z[y][x][sign])
  + if (ZX >= buffer->z[y][x][sign])
  {
  - buffer->z[y][x][sign] = z;
  + buffer->z[y][x][sign] = ZX;
  buffer->overdraw[y][x][sign]++;
  }
  }
  