minor comment fixes

This function was removed in ce2fe9d3.

de-bitrot CI

Seems the M1 and/or Ventura images need root when installing things.

The base OS for this image is old enough that authentication for installing
packages on it no longer works.

Testing on Intel macOS is no longer supported by Cirrus.

Testing on anything except the latest macOS is proving impractical.

misc updates and clean up

This also switches to installing the package rather than download the sources
and building them. Should be slightly faster.

This comment was written as if it were describing 4-level paging, where the
useful pointer bits are 48.

Debian: #1017199 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1017199


Reported-by: Lucas Nussbaum <lucas@debian.org>

CI: upgrade images

minor improvements

The images/infrastructure for this are dead.

From the CMake docs, I think we should have been doing this all along.
Everything seemed to work out because the GMP headers are relatively clean.

Linux 4.11 added `statx`, which it seems libc now uses in preference to some of
the older stat calls on 32-bit architectures.

Reported-by: Adrian Bunk <bunk@debian.org>
Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1004035

Newer kernels/libc use this in preference to `stat`/`fstat`.

Reported-by: Lucas Nussbaum <lucas@debian.org>

Debian: #1002186 “rumur: FTBFS”
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1002186

This aids reproducible builds, which we have gradually been progressing towards.

At this point it seems unlikely the Flex bug¹ that prevents using
`%option noline` will ever be fixed. So lets just use the work around for it.

¹ https://github.com/westes/flex/issues/268