Test STXR-ctrl

AArch64 STXR-ctrl
{
0:X1=x; 0:X3=y;
1:X0=y; 1:X5=x;
}
 P0          | P1              ;
 MOV W0,#2   | MOV W2,#2       ;
 STR W0,[X1] |                 ;
 DMB ST      | LDXR W1,[X0]    ;
 MOV W2,#1   | STXR W3,W2,[X0] ;
 STR W2,[X3] | CBNZ W3,Fail    ;
             | MOV W4,#1       ;
             | STR W4,[X5]     ;
             | Fail:           ;
Observed
    y=2; x=2; 1:X3=0; 1:X1=1;