MFC r309364 r309367 r309624

locale: fix buffer management

Also, handle signed and unsigned chars, and more gracefully handle
invalid input.

locale: enable more warnings; fix them

Do not set WARNS, so it gets the current default of 6.
Fix the warnings by sprinkling static, const, or strdup.
Make some constant data tables const. Fix whitespace.

Sponsored by: Dell EMC