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>
diff --git a/qemu-thread-win32.c b/qemu-thread-win32.c
index 3524c8b..177b398 100644
--- a/qemu-thread-win32.c
+++ b/qemu-thread-win32.c
@@ -330,7 +330,7 @@
     return handle;
 }
 
-int qemu_thread_is_self(QemuThread *thread)
+bool qemu_thread_is_self(QemuThread *thread)
 {
     return GetCurrentThreadId() == thread->tid;
 }