unix: fix coredump bit on aix/ppc64

Change-Id: Id7a299f240bf1d6394c7d2acb6fd93b9f8f6ca27
Reviewed-on: https://go-review.googlesource.com/c/sys/+/192359
Run-TryBot: Clément Chigot <clement.chigot@atos.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/syscall_aix.go

@@ -350,7 +350,7 @@ func (w WaitStatus) Signal() Signal {
 
 func (w WaitStatus) Continued() bool { return w&0x01000000 != 0 }
 
-func (w WaitStatus) CoreDump() bool { return w&0x200 != 0 }
+func (w WaitStatus) CoreDump() bool { return w&0x80 == 0x80 }
 
 func (w WaitStatus) TrapCause() int { return -1 }