[Perl/perl5] 22c3e2: locale.c: Only define a structure if needed

[Karl Williamson via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 22c3e2b642f9c6c6765d1d0fc67c10a59ca8a7f0
      
https://github.com/Perl/perl5/commit/22c3e2b642f9c6c6765d1d0fc67c10a59ca8a7f0
  Author: Karl Williamson <k...@cpan.org>
  Date:   2023-08-09 (Wed, 09 Aug 2023)

  Changed paths:
    M locale.c

  Log Message:
  -----------
  locale.c: Only define a structure if needed

Without LC_NUMERIC, this structure is unused, and generates a compiler
warning.