GNU programs may expect the GNU version of basename, which has a
different prototype (argument is const-qualified) and prototype it
themselves too. of course if they're expecting the GNU behavior for
the function, they'll still run into problems, but at least this
eliminates some compile-time failures.

note that it still will have the standards-conformant behavior, not
the GNU behavior. but at least this prevents broken code from ending
up with truncated pointers due to implicit declarations...

this should be everything except for some functions where the non-_l
version isn't even implemented yet (mainly some non-ISO-C wcs*
functions).

programs that use this tend to horribly botch international text
support, so it's questionable whether we want to support it even in
the long term... for now, it's just a dummy that calls strcmp.