For historical reasons MinGW used to define a higher value for
_WIN32_WINNT. Over years of refactoring this turned into a _lower_
value, which has then started breaking compilation on MinGW. This
change gets ride of the MinGW specific value.

R: mlippautz@chromium.org
Bug: V8:12099
Change-Id: Ic24b71c6767cd4d1b53a6cb6487517dec614cd1a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3123639Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76545}