support %token_table declaration). Originally the port was relying on
bison(1) instead (via USES=bison) in yacc-compat mode, but was switched
to yacc(1) in r389653 because it failed to build against `devel/bison'
version update to 3.0.4 as part of an exp-run (see PR).
It turns out that actually generated code does not suffer from removing
%token_table: the only difference in generated `neural_parse.cc' is that
yyname[] table is not guarded by `#if YYDEBUG' and it #define's yytname
as yyname, but the code that references yytname in `neural_parse.cc' is
#if'ed 0 and YYDEBUG is defined to 1 earlier. That said, simply comment
out %token_table line which allows the build to proceed (ir)regardless of
the yacc(1) version, on all FreeBSD releases (including 8.X).
While here, remove `ac_cv_lib_stdcpp_main=no' in CONFIGURE_ENV that was
supposed to fix the build against Clang added in r323095 as it seems no
longer required, augment COMMENT and port description, and fix WWW line
to point to working website, killing trailing whitespace along the way.
PR: 200833
