qemu-thread: use pthread_equal

Fixes

qemu-thread.c: In function `qemu_thread_equal':
qemu-thread.c:161: error: invalid operands to binary ==

Use of pthread_equal suggested by Filip Navara.

Signed-off-by: Sebastian Herbszt <herbszt@gmx.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
