trace: use glib atomic int types

trace: use glib atomic int types

Juan reported that RHEL 6.4 hosts give compiler warnings because we use
unsigned int while glib prototypes use volatile gint in trace/simple.c.

  trace/simple.c:223: error: pointer targets in passing argument 1 of 'g_atomic_int_compare_and_exchange' differ in signedness

These variables are only accessed with glib atomic int functions so
let's play it by the book and use volatile gint.

Reported-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1360676045-9204-2-git-send-email-stefanha@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>