In summary,
* The build was successful, and all tests passed on:
Ubuntu 22.04, Debian 11.1, CentOS 8-stream, Manjaro 17, GNU/Hurd, Cygwin.
* The build was successful, with 21 test failures (mostly crashes) on:
Debian 9.1, FreeBSD 11, NetBSD 9, Solaris 11 OmniOS, Solaris 11 OpenIndiana,
macOS 12.5.
* The build was successful, with 1 test failure on:
OpenBSD 6.5.
* The build failed with a link error on:
Alpine Linux 3.17.
* I could not build because the Boehm GC has 2 test failures on:
OpenSUSE Leap 15.2.
* I could not build because libpaper-2.0.5 did not compile, not even with
attempted workarounds, on:
Solaris 10, Solaris 11.4, AIX 7.1.
* I did not attempt a build since the other platforms should work first, on:
mingw.
Many thanks for all your help here. I (think I)'ve fixed a lot of the problems; a few I couldn't see anything to act on.
I'll make a new alpha release once I've finished working on libpaper (which you've also kindly tested and made many bug reports about).