Don't count mv->z, only vtx->z within 0,0 & 1024,1024.

- Clipping is done on the SH4 side, garbage might be outside the screen
- Mod vols aren't drawn anyway for now
- I wonder how much does this cost on the rend-thread?
Force block (header) checks by default.

- Unstable opts disables them (and only lets hard-coded places)
- This fixes shenmue (and possibly many other dynarec crashes)
Fix gcw and nacl makefiles abit
Don't count Z for modvols
(partial merge of zhack, the parts that have no speed hit)