gcc ignores locale (no UTF-8 source code supported)

[Benjamin Kosnik]

> You could autoconf for the existence of the wide character routines.

FYI: libstdc++-v3 already has done this. Feel free to take the
relevant bits from libstdc++-v3/acinclude.m4:894

GLIBCPP_CHECK_WCHAR_T_SUPPORT

-benjamin