[Perl/perl5] efb3e7: Force windows into C++ mode

[Karl Williamson via perl5-changes]

  Branch: refs/heads/smoke-me/khw-c99
  Home:   https://github.com/Perl/perl5
  Commit: efb3e7c11633ab7dbb5e0f91d03dcf4674043a35
      
https://github.com/Perl/perl5/commit/efb3e7c11633ab7dbb5e0f91d03dcf4674043a35
  Author: Karl Williamson <k...@cpan.org>
  Date:   2020-10-07 (Wed, 07 Oct 2020)

  Changed paths:
    M win32/Makefile

  Log Message:
  -----------
  Force windows into C++ mode