Move zafl vars before shared map

afl-showmap has a problem that it doesn't obey AFL_MAP_SIZE and just creates a 4mb map. this creates an incompatibility with zafl, as zafl stores some variables at map_addr+map_size. Since afl-showmap over-allocates the map, it conflicts with the zafl variables and libzafl can't do the mapping it needs. This MR will fix the issue with afl-showmap by moving zafl variables to 1 page before the fixed map.