[tlbuild] How to compile BibTeX from source?

[Henri Menke]

Dear list,

The Makefile in source/extra/bibtex/ only builds documentation and no executable
and on CTAN there is no Makefile or even build instructions available.  How can
I build BibTeX from source?  I guess I start with

    $ tangle bibtex.web

to obtain bibtex.p but where do I go from there?  What kind of Pascal compiler
do I need?  Can I use Free Pascal (https://www.freepascal.org/)?  How to set
compilation flags, like 'trace' or 'debug' mode?

Thanks for your help,
Henri