This adds tests for something I fixed ‘by mistake’ in
efcf35c4, which
occurs from 5.8.0 to 5.15.5:
$ perl5.15.4 -le '
use warnings "uninitialized";
use constant {u=>undef,v=>undef};
sub foo(){u} sub foo(){v}
'
Use of uninitialized value at -e line 1.
Use of uninitialized value at -e line 1.
__END__
EXPECT
Use of uninitialized value in addition (+) at - line 3.
+########
+use warnings 'uninitialized';
+use constant {u=>undef, v=>undef};
+sub foo () {u}
+sub foo () {v}
+EXPECT