GLib g_get_real_time() is an alternative to gettimeofday() which allows
to simplify our code.

For semihosting, a few bits are lost on POSIX host, but this shouldn't
be a big concern.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20220307070401.171986-5-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>