[Perl/perl5] fd4b7d: Mingw compiled with UCRT is locale thread-safe

[Karl Williamson via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: fd4b7dbea2a88d10f13abc7ed631961b32593200
      
https://github.com/Perl/perl5/commit/fd4b7dbea2a88d10f13abc7ed631961b32593200
  Author: Karl Williamson <k...@cpan.org>
  Date:   2023-09-18 (Mon, 18 Sep 2023)

  Changed paths:
    M perl.h

  Log Message:
  -----------
  Mingw compiled with UCRT is locale thread-safe

The previous libc routines used with this weren't, but the ones in UCRT
do have this capability.  Take advantage of them.