Expose thread_id in info cpus

Based on patch by Glauber Costa:

To allow management applications like libvirt to apply CPU affinities to
the VCPU threads, expose their ID via info cpus. This patch provides the
pre-existing and used interface from qemu-kvm.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

os-win32.c

@@ -266,3 +266,8 @@ int qemu_create_pidfile(const char *filename)
     }
     return 0;
 }
+
+int qemu_get_thread_id(void)
+{
+    return GetCurrentThreadId();
+}