Handle additional syscall cases/terminator instructions

[boomanaiden154]

There are other ways to make syscalls on X86, including int 0x80, and sysenter that we should probably also be sanitizing for security reasons.

We also need to make sure that we're taking care of all terminator instructions. We seem to be, but changing to MCInstrDesc::isTerminator probably makes a lot of sense and avoids us needing to manually handle the cases.