Freeciv

The new Makefile.in.in places new requirements for the make implementation to use, so we need to be careful with the stable branches. It seems no brainer that we can't take the change to S3_1. We can take even breaking change to S3_3. In between is S3_2, which isn't clearly in either side. I'm inclined to take the change in as 1) it might turn necessary for compatibility with currently-future components during S3_2 lifetime, 2) preferred build system in S3_2 is meson, so autotools breakage is not as fatal as with earlier branches, and 3) S3_2 has not seen stable release yet, so we are not as bound to keep compatibility with tools that have been able to build freeciv with earlier releases of the series as after there are some actual stable releases to compare to.