qemu-thread.h: include inttypes.h

qemu-thread.h relies on uint64_t being defined, but doesn't include
inttypes.h explicitly. This makes it easier to use it from vscclient (part
of libcacard).

qemu-thread.h

 #ifndef __QEMU_THREAD_H
 #define __QEMU_THREAD_H 1
 
+#include <inttypes.h>
+
 typedef struct QemuMutex QemuMutex;
 typedef struct QemuCond QemuCond;
 typedef struct QemuThread QemuThread;