nptl: i386 needs atomic.h for atomic_exchange_acq

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libpthread/nptl/sysdeps/unix/sysv/linux/i386/lowlevellock.h

@@ -26,6 +26,7 @@
 # include <bits/pthreadtypes.h>
 # include <bits/kernel-features.h>
 # include <tcb-offsets.h>
+# include <atomic.h>
 
 # ifndef LOCK_INSTR
 #  ifdef UP