Test MP+o-wb-o+o-data-o

LISA MP+o-wb-o+o-data-o
(*
 * Allowed: wmb on only two threads with write-to-read relationship,
 * but the data dependency on P1 is not enforced by either r[lderef],
 * r[deref], or f[rb_dep].  This would therefore be allowed on real
 * hardware, namely DEC Alpha.
 *)
{
x = 2;
p = a;
0:r1=x;
}
 P0           | P1                 ;
 w[once] x 4  | r[once] r1 p       ;
 f[wmb]       | r[once] r2 r1      ;
 w[once] p r1 |                    ;
Observed
    1:r2=2; 1:r1=x;