Fix unlink() for STATUS_DELETE_PENDING on Windows.

Commit f357233c assumed that it was OK to return ENOENT directly if
lstat() failed that way.  If we got STATUS_DELETE_PENDING while trying
to unlink a file that we had already unlinked successfully once before
but someone else still had open (on a kernel version that has "pending"
unlinks by default), then we would no longer reach the retry loop in
pgunlink().  That loop claims to be only for handling sharing violations
(a different phenomenon), but the errno is the same.

Restore that behavior with an explicit check, to see if it fixes the
occasional 'directory not empty' failures seen in the pg_upgrade tests
on CI.  Further improvements are possible with proposed upgrades to
modern Windows APIs that would replace this convoluted code.

Reported-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/20220920013122.GA31833%40telsasoft.com
Discussion: https://postgr.es/m/CA%2BhUKG%2BajSQ_8eu2AogTncOnZ5me2D-Cn66iN_-wZnRjLN%2Bicg%40mail.gmail.com

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