meson -Drust=enabled fails on macOS without GNU sed

I think it's due to e509b5b8be (rust: support for Windows, 2025-10-15) [relevant folks CC'd], where we assume sed can take "-s" (which AFAICT is a GNU extension). But perhaps "-n" was intended with a "p" flag on the substitution?

I've been building with Rust enabled on Gentoo now for a minute and haven't hit any issues, but that's perhaps because the command is running with "-s" and not working as intended (yet still producing the expected results).

The relevant snippet is this (reformatted slightly by GMail, apologies):

case "$(cargo -vV | sed -s 's/^host: \(.*\)$/\1/')" in
  *-windows-*) LIBNAME=gitcore.lib;;
  *) LIBNAME=libgitcore.a;;
esac

but "cargo -vV" produces something like

cargo 1.89.0 (c24e10642 2025-06-23) release: 1.89.0 commit-hash: c24e1064277fe51ab72011e2612e556ac56addf7 commit-date: 2025-06-23 host: x86_64-apple-darwin libgit2: 1.9.0 (sys:0.20.2 vendored) libcurl: 8.7.1 (sys:0.4.80+curl-8.12.1 system ssl:(SecureTransport) LibreSSL/3.3.6) ssl: OpenSSL 3.5.0 8 Apr 2025 os: Mac OS 12.7.6 [64-bit]

(on my older system, on which I haven't tried the build; the failure is on my newer system with close-enough-to-the-same output). I'm sure you can see why I don't understand why we need GNU's "-s" ("consider files as separate rather than as a single, continuous long stream") here?