report: widen scope of #ifndef

This commit moves a #ifndef _WIN32 to contain the entire if
statement that inspects file descriptors. Prior to this commit,
the #ifndef was inside the if, making it essentially dead code
on Windows.

PR-URL: https://github.com/nodejs/node/pull/25960


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>