Fix compatibility with current GNU Make (and Ubuntu 26.04)

[adamnovak]

Changelog Entry

To be copied to the draft changelog by merger:

• vg now builds with GNU Make 4.4.1, as on Ubuntu 26.04
• vg now uses system libelf/libdw
• vg now ships its own Cairo and pixman libraries as submodues, to enable static builds on modern Ubuntu. These build with Meson; if needed, a new enough Meson will be installed on older Ubuntu via pipx by make get-deps.
• Reverted Pin back binfmt to work around https://github.com/tonistiigi/binfmt/issues/298 #4926 due to crashes in the compiler in the emulated builds
• vg Docker containers are now built on top of Ubuntu 26.04

Description

GNU Make removed the hack we were using to run a rule at Makefile startup (claiming that it would generate an include-able Makefile fragment, marking it .PHONY so it would always run, and telling Make not to complain if the file to be included didn't exist). It's not mentioned in the project's NEWS file, but it happened between 4.3 and 4.4.1.

This converts half of that target to $(shell ) calls (the half that needs a bunch of Make-level variables), and the other half to a shell script (the half where we need to enforce success).

[adamnovak]

This still doesn't fix 26.04, because the compiler there doesn't like something in libelf:

riscv_disasm.c: In function 'riscv_disasm':
riscv_disasm.c:1259:46: error: initialization discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
 1259 |                   struct known_csrs *found = bsearch (&key, known,
      |                                              ^~~~~~~

[adamnovak]

This will need vgteam/structures#15 and vgteam/libbdsg#242

[adamnovak]

I don't think we'll be able to get the Docker build logs from CI without fixing or working around greg7mdp/sparsepp#98.

When I run the Docker build locally on my Mac I get a complaint at the final link step that there's something wring with libvcfh.a:

3.971 /usr/bin/aarch64-linux-gnu-ld.bfd: /vg/lib/libvcfh.a: error adding symbols: archive has no index; run ranlib to add one
3.990 collect2: error: ld returned 1 exit status
3.990 make: *** [Makefile:551: lib/vg_is_static] Error 1

This happens even if I stick a ranlib call into the command used to build it.

[adamnovak]

If we want the Docker to ship a static binary, which we pull out and use for our static ARM release and for putting in a new, smaller Docker container, then we can't upgrade past 22.04 until https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1104888 is fixed and shipped in an Ubuntu release, since in 24.04 and on Ubuntu no longer packages a libcairo.a anywhere.

Or else we need to pull in Cairo as a submodule or otherwise provide a source build of Cairo for the Docker container.

[adamnovak]

OK I have no idea why the docs build job can't find vgteam/libbdsg@5429995 which is merged in over there. And it looks like the updated libelf is not happy back on 22.04?

I will have to come back to this.

[adamnovak]

I have finally fixed the docs job, but my approach makes the docs job almost twice as long as the fix in #4870. So we probably want to use that one when they conflict.

[adamnovak]

There's still a problem where the Meson in the CI base image is too old to build Cairo/pixman. I think I need to also switch the CI prebake image over to a newer Ubuntu.