sim: add checks to core headers to prevent incorrect common building

sim: add checks to core headers to prevent incorrect common building

Some of the core sim headers rely on the SIM_AC_OPTION_BITSIZE macro
which can change the size of core types.  Since these haven't been
unified across ports, add checks to make sure they aren't accidentally
included when building for all ports.  This caught the sim-load file
using poisoned headers that it didn't actually need.