Deal with make dramadirs issue in zsh. Support C++20

  "eval `make dramadirs`" was no longer working on ZSH (at least 5.3 and later)
       The only way to get the sequence to work was to add comment line
       before the first export line and I can't automate that.  I suspect
       we can now se a prefix "export" on all machines of interest so
       have move to that approach.  Most likely issue would be solaris!

    Support C++20.

   ACMM Version 5.22.