cdecl99: Avoid gnulib setlocale_null bits.

cdecl99: Avoid gnulib setlocale_null bits.

As this is a single-threaded application which does nothing exciting
regarding locales, we shouldn't need the setlocale_null replacement.
This performs a pile of configure tests related to the thread safety
of setlocale(x, NULL), which includes possibly pulling in threading
libraries and a bunch of other nonsense.

To do this, we replace hard-locale (the only module using this) with
an inline function using setlocale directly (inline is much better,
because there is only one call site).