The approach of system_hooks has dependency to npth (which is not needed, essentially).
Now, given `gpgrt_get_syscall_clamp` API, we can avoid entire system_hooks usage.
The new way will be:
- libassuan side:
- When system_hooks is set by an application, prefer that
- Not set, get pre and post camp functions by `gpgrt_get_syscall_clamp` and wrap the calls to `__assuan_` functions with them.
- Applications can remove setting of system_hooks, only set the clamp functions