Make stacked -l work

Make stacked -l work

Perl 5.10.0 introduced stacked filetest operators,

   -x -r $foo

being equivalent to

    -r $foo && -x _

That does not work with -l.  It was these suspicious lines in
Perl_my_lstat_flags that drew my attention to it:

>     else if (PL_laststype != OP_LSTAT
> 	    && (PL_op->op_private & OPpFT_STACKED) && ckWARN(WARN_IO))
> 	Perl_croak(aTHX_ no_prev_lstat);

That croak only happens when warnings are on.  Warnings are just
supposed to be warnings, unless the ‘user’ explicitly requests
fatal warnings.

$ perl -le 'print "foo", -l -e "miniperl"'
foo
$ perl -lwe 'print "foo", -l -e "miniperl"'
The stat preceding -l _ wasn't an lstat at -e line 1.

That it doesn’t die in the first example is a bug.

In fact, it’s using the return value of -e as a file name:

$ ln -s miniperl 1
$ ./miniperl -le 'print -l -e "miniperl"'
1

And, with warnings on, if the preceding stat *was* an lstat, it
falls back to the pre-stacked behaviour, just as it does when warn-
ings are off.

It’s meant to be equivalent to -e "miniperl" && -l _ (which is why the
error message above says ‘The stat preceding -l _’).