qemu-thread: Let qemu_thread_is_self() return bool

qemu_cpu_is_self(), passing the return value through, will later be
adapted to return bool as well.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Stefan Weil <sw@weilnetz.de>

qemu-thread-posix.c

@@ -151,7 +151,7 @@ void qemu_thread_get_self(QemuThread *thread)
     thread->thread = pthread_self();
 }
 
-int qemu_thread_is_self(QemuThread *thread)
+bool qemu_thread_is_self(QemuThread *thread)
 {
    return pthread_equal(pthread_self(), thread->thread);
 }