Implement assigning xor (^^=) operator

When I added '^^' I forgot to implement or test the assigning version of
it.

Also it seems `pp_xor` had the left and right arguments round the wrong
way; but until the asymmetry introduced by this change nobody had
noticed before. This is now fixed.

Author: leonerd

pp_ctl.c

@@ -2172,11 +2172,12 @@ Perl_die_unwind(pTHX_ SV *msv)
 
 PP(pp_xor)
 {
-    SV *left  = PL_stack_sp[0];
-    SV *right = PL_stack_sp[-1];
-    rpp_replace_2_IMM_NN(SvTRUE_NN(left) != SvTRUE_NN(right)
-                    ? &PL_sv_yes
-                    : &PL_sv_no);
+    SV *left  = PL_stack_sp[-1];
+    SV *right = PL_stack_sp[0];
+    bool ret = SvTRUE_NN(left) != SvTRUE_NN(right);
+    rpp_replace_2_IMM_NN(boolSV(ret));
+    if (PL_op->op_flags & OPf_STACKED)
+        sv_setbool(left, ret);
     return NORMAL;
 }
 

t/op/lop.t

@@ -10,7 +10,7 @@ BEGIN {
     set_up_inc('../lib');
 }
 
-plan tests => 47;
+plan tests => 57;
 
 for my $i (undef, 0 .. 2, "", "0 but true") {
     my $true = 1;
@@ -105,6 +105,10 @@ for my $test (
     my ($a,$b, $exp) = @$test;
     is(($a xor $b), $exp, "($a xor $b) == '$exp'");
     is(($a ^^ $b), $exp, "($a ^^ $b) == '$exp'");
+
+    my ($lhs, $rhs) = @$test;
+    $lhs ^^= $rhs;
+    is($lhs, $exp, "$a ^^= $b gives '$exp'");
 }
 
 # precedence

toke.c

@@ -6097,6 +6097,10 @@ yyl_caret(pTHX_ char *s)
             TOKEN(0);
         }
         pl_yylval.ival = OP_XOR;
+        if (*s == '=') {
+            s++;
+            OPERATOR(ASSIGNOP);
+        }
         OPERATOR(OROR);
     }
     if (bof && s[1] == '.')