devel/tcltls: fixes to the newly-added generation of DH-parameters
Specifically:
- move the entire code to the post-configure target -- so
that our own header will be newer than the Makefile generated by configure. Otherwise the authors' Makefile will (attempt to) regenerate the dh_param.h again.
- use openssl's asnparse functionality to more reliably
parse the generated prime -- and turn it into C.
PR: 275160