[Unison-hackers] makefile rototill (now portable!), opam pending change

[Greg Troxel]

Tõivo has just improved and simplified our makefiles, so they build with
BSD make and nmake, in addition to gmake, and probably some others.
I've already merged this -- of course it passes CI.  It works for me on
NetBSD, with gmake or BSD make, with or without -j32.  Wider testing
would be great.

There's a pending change to unison.opam.  I'd appreciate comments from
people that know opam better than I do :-) Absent comments, I'll merge
it on the 26th.

  https://urldefense.com/v3/__https://github.com/bcpierce00/unison/pull/1100__;!!IBzWLUs!TfAwGPCILK0w9k5w9Jpaoqmt7MeN07uT3LkdxhiE7BAIcjvG_pBZSuciLQFWEe0uxm0JUxpT3Rkwe6DRHYY59EGE$ 

This does not mean a release is imminent.   While a little scary in the
details, this rototill doesn't really change anything, and we just had
2.53.7.