Because NCHARS is (256+3) cc->cc_func(i) was called with 256, 257
and 258 as argument leading to possible undefined behaviour (at
least on NetBSD with non-C locale (e.g. `en_US.UTF-8') this led to
only honoring one `[:...:]' character class in bracket expressions).
The old ytab.o rule produced ytab.c and ytab.h too, but this wasn't
visible as dependencies, so make -j would fail. Make this explicit, and
use the implicit .c.o rule rather than writing out the $(CC) command.