wc: 3× speedup in C locale

wc: 3× speedup in C locale

The 3× speedup was measured by invoking 'wc $(find * -type f)'
on the coreutils sources etc. on an Ubuntu 23.04 x86-64.
These changes also speed up wc 20% in UTF-8 locales.
* src/wc.c (wc_isprint, wc_isspace): New static vars.
(wc): Use them for speed.
(main): Initialize them if needed.
(isnbspace): Remove; no longer used.