regex: port to OS X 10.8.5 en_US.UTF-8 locale

This fixes a bug when ignoring case and when comparing the
titlecase letter 'ǈ' (U+01C8 LATIN CAPITAL LETTER L WITH SMALL
LETTER J) to the corresponding uppercase letter 'Ǉ' (U+01C7 LATIN
CAPITAL LETTER LJ).  In the OS X 10.8.5 en_US.UTF-8 locale, the
titlecase letter is neither lowercase nor uppercase, but
uppercasing the titlecase letter (via towupper) yields the
uppercase letter, so the two letters should match when ignoring case.
Problem reported by Jim Meyering in <http://debbugs.gnu.org/16911#16>.
* lib/regex_internal.c (build_wcs_upper_buffer, build_upper_buffer):
Don't test whether a character is lowercase before uppercasing it.