fix Getdirentries: base comes back in r2.

R=rsc
DELTA=3  (3 added, 0 deleted, 0 changed)
OCL=24727
CL=24727

src/lib/syscall/file_darwin.go

@@ -96,5 +96,8 @@ func Dup2(fd1, fd2 int64) (ret int64, errno int64) {
 
 func Getdirentries(fd int64, buf *byte, nbytes int64, basep *int64) (ret int64, errno int64) {
 	r1, r2, err := Syscall6(SYS_GETDIRENTRIES64, fd, int64(uintptr(unsafe.Pointer(buf))), nbytes, int64(uintptr(unsafe.Pointer(basep))), 0, 0);
+	if r1 != -1 {
+		*basep = r2
+	}
 	return r1, err;
 }