Add VM-based CI that builds and tests on DragonFly BSD

[neilpang]

Closes #1418

#1418 asked for a drop-in test build on FreeBSD and other operating systems using
the vmactions VMs. This adds that workflow as a separate file, so it neither
interferes with nor delays the Azure Pipelines matrix.

What the job does

It runs the guest OS in a VM on an ubuntu-latest runner, builds MoarVM, then
builds NQP against it and runs the NQP test suite -- MoarVM has no test suite of its
own (make test just prints build/test.txt).

Verification run on the exact head of this branch:
https://github.com/neilpang/MoarVM/actions/runs/30349845037 -- 371 compiles,
This is MoarVM version 2026.07-7-ge82d6372a built with JIT support,
Files=145, Tests=13476 ... Result: PASS. The job takes about 5 minutes end to end.

Two things in the job need explaining:

• --toolchain=gnu. build/setup.pm maps the BSDs to the bsd toolchain, but
  the Makefile that generates cannot be built by BSD make: the object rules use
  $*.c, and BSD make expands $* to the file name without its directory, so
  every compile fails with clang: error: no such file or directory: 'args.c'
  (run). If you would
  rather have the native make path work, the fix is in the $*.c occurrences in
  build/Makefile.in; happy to send that separately.
• no -j on the MoarVM build. The vendored dyncall build shells out to the base
  system make, which rejects the bare -j that GNU make puts into MAKEFLAGS for
  its job server: make[1]: illegal argument to -j -- must be positive integer!

Why only DragonFly BSD

I tried FreeBSD, OpenBSD, NetBSD and Solaris as well. Each is blocked by a real
portability break rather than by CI configuration, so I left those jobs out instead
of landing a red workflow.

FreeBSD -- 3rdparty/libuv (pinned at MoarVM/libuv@dcd3a3f, the head of
1-50-0-with-pty) has:

#if defined(__DragonFly__) || defined(__FreeBSD__) || \
    defined(__NetBSD__) || defined(__OpenBSD__)
#include <util.h>
#endif

FreeBSD has no <util.h> -- openpty(3) is declared in <libutil.h> and lives in
-lutil. Confirmed absent on 13.5, 14.3 and 15.1, with libutil.h present on each:
run.

Two changes make FreeBSD work, both verified:

1. MoarVM/libuv: use <libutil.h> on FreeBSD -- PR: unix: include <libutil.h> for openpty() on FreeBSD libuv#1. With it,
   MoarVM builds and the NQP suite passes on 13.5, 14.3 and 15.1:
   run.
2. build/setup.pm: add util to the FreeBSD syslibs. Without it
   libmoar.so carries an unresolved openpty; the build and the NQP suite still
   pass because nothing in them spawns a pty, but a pty spawn would fail at runtime
   (run). Adding
   util links libutil.so.9 on 13.5 and libutil.so.10 on 15.1
   (run).

I can send the setup.pm change and the FreeBSD job as a follow-up once the libuv
side is settled.

NetBSD and OpenBSD -- 3rdparty/zmij does not compile:

3rdparty/zmij/zmij.c:2076:45: error: 'DBL_DECIMAL_DIG' undeclared
3rdparty/zmij/zmij.c:2076:63: error: 'FLT_DECIMAL_DIG' undeclared

and on NetBSD additionally
zmij.c:151:24: error: expected declaration specifiers or '...' before '__builtin_constant_p'
-- NetBSD's <sys/bswap.h> defines bswap64 as a macro, colliding with zmij's
static inline of the same name. Runs:
OpenBSD,
NetBSD. This arrived
with the Ryu -> Zmij switch (#1986).

Solaris 11.4 -- src/core/args.c:75:33: error: implicit declaration of function 'alloca';
Solaris declares alloca in <alloca.h>.
Run.

Also in this PR

• README gains a badge for the new workflow, next to the Azure one.
• actions/checkout@v7, the current major.
• Both checkouts use fetch-depth: 0 + fetch-tags: true: Configure.pl takes the
  version from git describe --tags, and NQP refuses a MoarVM older than its pinned
  MOAR_REVISION.
• The run script sets safe.directory, because the tree is synced into the VM and
  ends up owned by a different uid than the build runs as.

[Copilot]

Pull request overview

Adds a new GitHub Actions workflow that runs MoarVM + NQP build/test inside a DragonFly BSD VM (via vmactions) on ubuntu-latest, providing CI coverage for a non-hosted platform without impacting the existing Azure Pipelines matrix.

Changes:

• Introduces .github/workflows/test_other_platforms.yml to build MoarVM and run the NQP test suite on DragonFly BSD within a VM.
• Updates README.md to include a GitHub Actions badge for the new workflow.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
README.md	Adds a status badge pointing to the new “Test on other platforms” workflow.
.github/workflows/test_other_platforms.yml	New VM-based CI job that builds MoarVM and runs NQP tests on DragonFly BSD.

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