Try to unbreak 021_row_visibility.pl on mingw.

Try to unbreak 021_row_visibility.pl on mingw.

Thanks to Andrew for proposing and testing this fix.

It's possible that we should address this on a more fundamental basis,
e.g. by configuring PerlIO to to CR/LF conversion for us, but this
approach already exists in other places. And it's nice to unbreak the
BF.

Proposed-By: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
Discussion: https://postgr.es/m/2355d1f0-0244-da9c-ef0c-7542b944e1ac@2ndQuadrant.com