dthelp/parser/pass1: get it to build

dthelp/parser/pass1: get it to build

So this is going to be tricky/painful getting this parser fully
operational.  It's pretty hairy with various interdependencies and
generated code.

It's rather complicated how each sub dir depends on the previous one.
Also, the parser subdir has dependencies on the helptag subdir, and
vice-versa, so some hackery was needed to get that to work.

Due to the wierd interdepencencies between helptag and parser,
we disable parallel builds there.

This is some really horrible code and design - not surprising since it
dates to 1989.

I think it should just be removed -- who can maintain or refactor this
code?

Also, dthelp_htag1 is now built in pass1/parser/, not in
pass1/helptag/ as it used to be.