Many ports have the same sim syscall logic, so add some helpers to handle
all the common details. The arches still have to deal with the unpacking
and packing of the syscall arguments, but the rest of the sim<->callback
glue is now shared.
The syscall path was the only code checking the custom exception state
after recent cleanups. Once we change that to the common engine halt
function, we can delete that state entirely.
This also helps highlight some other dead code that we can cull.
genericXor, genericBtst): Use `unsigned32'.
* op_utils.c: Likewise.
* mn10300.igen, am33.igen: Use `unsigned32', `signed32',
`unsigned64' or `signed64' where type width is relevant.
