Configure: Allow LC_ALL syntax override

[khwilliamson]

Fixes #22992

The problem here had to do with cross-compilation. There was no way to override Perl's calculation of how LC_ALL is represented. I had not put one in because it is hard to get it right manually. But this doesn't work in cross-compilation; it's better to have a difficult-to-get-right way than no way at all.

I don't know where to document this. You need to specify in a hints file:

   perl_lc_all_separator="correct-value"
   perl_lc_all_category_positions_init="correct-value"

• This set of changes likely requires a perldelta entry