[samm-git]

What does this PR do?

Marks FreeBSD executables that create V8 isolates with
NT_FREEBSD_FCTL_WXNEEDED via elfctl(1): mksnapshot, node_mksnapshot,
and node.

Motivation

With kern.elf{32,64}.allow_wx=0, FreeBSD rejects RWX mappings with EACCES.
V8 pre-maps its code range RWX, so Node and the snapshot generators abort with:

# Check failed: 12 == (* __error()).

ENOMEM is 12 and EACCES is 13 — the CHECK expects the wrong error.

-Wl,-z,wxneeded does not work on FreeBSD: lld emits
PT_OPENBSD_WXNEEDED, but FreeBSD checks NT_FREEBSD_FCTL_WXNEEDED.

Implementation

• Add tools/freebsd-wxneeded.py, a helper around elfctl -e +wxneeded.
• Mark mksnapshot and node_mksnapshot before their gyp actions run.
• Add a FreeBSD-only node_wxneeded target, part of all, to mark the linked
  node binary.

W^X remains enabled system-wide; only these JIT-using executables are exempt.

Testing

Full build on FreeBSD 15.1 arm64 with kern.elf64.allow_wx=0 succeeded.
elfctl reports wxneeded set on all three binaries, and the built Node runs
with the JIT enabled under W^X:

$ out/Release/node -e 'let s=0; for (let i=0;i<1e6;i++) s+=i;
                       console.log(process.version, s, /abc/.test("xabc"))'
v24.21.0 499999500000 true

node_wxneeded is part of all; building only make -C out node skips it.

Fixes: #40467

[nodejs-github-bot]

Review requested:

• @nodejs/gyp
• @nodejs/v8-update

[github-actions]

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[samm-git]

@MikeMcC399 rebased, thank you.

[MikeMcC399]

FreeBSD / x64 is listed as "experimental" and no longer tested in Jenkins CI.

Adding @nodejs/platform-freebsd team members with a request to review.