Add missing include guard to win32ntdll.h.

Thomas Munro <tmunro@postgresql.org>

Commit: ce14dbbcafde5a629d4dbcabdadecea440e7955d
Author: Thomas Munro <tmunro@postgresql.org>
Committer: Andrew Dunstan <andrew@dunslane.net>
Date: 2024-11-07T23:05:45Z
Releases: 14.14
Add missing include guard to win32ntdll.h.

Oversight in commit e2f0f8ed.  Also add this file to the exclusion lists
in headerscheck and cpluscpluscheck, because Unix systems don't have a
header it includes.

Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/2760528.1641929756%40sss.pgh.pa.us
(cherry picked from commit af9e6331aeba149c93052c3549140082a85a3cf9)

Author: Thomas Munro <tmunro@postgresql.org>
Author: Alexandra Wang <alexandra.wang.oss@gmail.com>

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