User-mode QEMU is not deterministic

QEMU in user-mode (linux-user or bsd-user) has no way to get the equivalent of the "-icount" argument found in softmmu mode.

It is true that some system calls in user-mode can prevent deterministic execution, but it would be very simple to patch time-related syscalls to return a number based on icount when in deterministic mode.

Putting both changes together (icount + time-related syscalls) would cover the needs for deterministic execution of most benchmarks (i.e., those not interacting with the network or other programs in the system).