[perl #78194] Make x copy PADTMPs in lv cx

So that \(("$a")x2) will give two references to the same scalar, the
way that \(($a)x2) does.

pp.c

@@ -1657,6 +1657,7 @@ PP(pp_repeat)
 	static const char* const oom_list_extend = "Out of memory during list extend";
 	const I32 items = SP - MARK;
 	const I32 max = items * count;
+	const U8 mod = PL_op->op_flags & OPf_MOD;
 
 	MEM_WRAP_CHECK_1(max, SV*, oom_list_extend);
 	/* Did the max computation overflow? */
@@ -1690,7 +1691,11 @@ PP(pp_repeat)
 		}
 #else
                if (*SP)
+                {
+                   if (mod && SvPADTMP(*SP) && !IS_PADGV(*SP))
+                       *SP = sv_mortalcopy(*SP);
 		   SvTEMP_off((*SP));
+		}
 #endif
 		SP--;
 	    }

t/op/repeat.t

@@ -156,7 +156,6 @@ is(77, scalar ((1,7)x2),    'stack truncation');
 is( (join ',', (qw(a b c) x 3)), 'a,b,c,a,b,c,a,b,c', 'x on qw produces list' );
 
 # [perl #78194] x aliasing op return values
-$::TODO = 'not fixed yet';
 sub {
     is(\$_[0], \$_[1],
       '[perl #78194] \$_[0] == \$_[1] when @_ aliases elems repeated by x')