The disasm framework reserves the private_data field for the disassemblers
themselves, not for people who use the disassembler. Instead, there is an
application_data field for callers such as the sim. Switch to it to avoid
random corruption/crashes when the disassemblers use private_data.
For targets that process argv in sim_create_inferior, improve the code:
- provide more details in the comment
- make the check for when to re-init more robust
- clean out legacy sim_copy_argv code
This will be cleaned up more in the future when we have a common inferior
creation function, but at least help new ports get it right until then.
