Fix a few bugs in the new extended locale functions.

Fix a few bugs in the new extended locale functions.
Move stub gettext functions to a stub libintl to make switching in
  gnu gettext easier.  Also add a few gnu-isms.
Change to using hidden names with global weak aliases for the extended
  locale functions, as expected by libstd++.
Slightly rework the locale data generation stuff to allow pregenerated
  locale data to be used with buildroot.