Don’t allow OPpTARGET_MY on postdec/inc
I was wrong in
9e319cc4f. postfix ++/-- writes to its return value
before reading its argument. If we optimise away the scalar
assignment in
$a = $b++;
(that’s what OPpTARGET_MY does), then $a gets written to before $b is
read. If $a and $b are the same, we get the wrong answer. This bug
has been present under ‘use integer’ since 5.6.0. I accidentally
extended it to non-integer ++/-- in
9e319cc4f.
(It’s not likely that someone will write $a = $b++, but it could hap-
pen inadvertently in more complex code.)