Test C11-B

AArch64 C11-B
"Example B from notes41"
{
0:X1=x;
1:X1=x; 1:X3=y;
2:X1=y; 2:X4=x;
}
 P0           | P1           | P2           ;
 MOV W0,#2    | LDR W0,[X1]  | MOV W0,#1    ;
 STLR W0,[X1] | DMB LD       | STLR W0,[X1] ;
              | LDAR W2,[X3] | MOV W2,#2    ;
              |              | STLR W2,[X1] ;
              |              | MOV W3,#1    ;
              |              | STLR W3,[X4] ;
exists
(x=2 /\ y=2 /\ 1:X0=2 /\ 1:X2=1)