[rive_native] Linux prebuilt artifacts require glibc 2.38 / GLIBCXX 3.4.32 — apps cannot even be linked on Ubuntu 22.04

Description

The prebuilt Linux artifacts published for rive_native are built against a
glibc 2.38 / GCC 13 toolchain, and they reference symbols that do not exist in
older glibc. Two consequences, the first of which I think is the more
important one:

1. A Flutter Linux app depending on rive cannot be built on Ubuntu 22.04
   at all. The link fails — this is not a runtime floor that a downstream
   project can choose to accept, it is a hard build-time requirement on the
   build host.
2. Apps built on a new enough host inherit a runtime floor of GLIBC_2.38 /
   GLIBCXX_3.4.32, because those requirements are baked into the prebuilt
   static libraries before the app's build starts.

Together these mean rive currently requires Ubuntu 24.04+ / Fedora 39+ /
Debian 13+ both to build against and to run on, and excludes every enterprise
and LTS distribution still in wide use — including the current Debian stable
and the previous Ubuntu LTS:

Distribution	glibc	libstdc++	Builds?	Runs?
RHEL / Rocky / Alma 9	2.34	GLIBCXX_3.4.29	no	no
Ubuntu 22.04 LTS (supported to 2027)	2.35	GLIBCXX_3.4.30	no	no
Debian 12 (bookworm)	2.36	GLIBCXX_3.4.30	no	no
Ubuntu 24.04 LTS	2.39	GLIBCXX_3.4.33	yes	yes

The build failure

Building a Flutter Linux release on ubuntu-22.04 (glibc 2.35, GitHub Actions
runner), Flutter 3.44.8, rive 0.14.8 → rive_native 0.1.8:

/usr/bin/ld: plugins/rive_native/librive_native_plugin.so: undefined reference to `__isoc23_strtoull'
/usr/bin/ld: plugins/rive_native/librive_native_plugin.so: undefined reference to `__isoc23_strtoll'
/usr/bin/ld: plugins/rive_native/librive_native_plugin.so: undefined reference to `__isoc23_strtol'
/usr/bin/ld: plugins/rive_native/librive_native_plugin.so: undefined reference to `__isoc23_strtoul'
/usr/bin/ld: plugins/rive_native/librive_native_plugin.so: undefined reference to `__isoc23_sscanf'
/usr/bin/ld: plugins/rive_native/librive_native_plugin.so: undefined reference to `std::ios_base_library_init()'
clang: error: linker command failed with exit code 1

__isoc23_* are the C23 header redirects glibc introduced in 2.38, and
std::ios_base_library_init() is GLIBCXX_3.4.32, i.e. GCC 13's libstdc++.
Neither exists on 22.04, so the link cannot resolve them.

Where the requirements come from

Verifiable from your published artifacts alone — no application code involved:

curl -sSLO "https://rive-flutter-artifacts.rive.app/rive_native_versions/0.1.8%2B1/rive_native_artifacts_linux.zip"
unzip -q rive_native_artifacts_linux.zip -d rive_linux
cd rive_linux/lib/release

$ for f in librive.a librive_pls_renderer.a librive_harfbuzz.a libluau_vm.a; do
    printf '%-24s %s\n' "$f" "$(strings -a $f | grep -o '__isoc23_[a-z]*' | sort -u | tr '\n' ' ')"
  done
librive.a                __isoc23_strtol
librive_pls_renderer.a   __isoc23_sscanf
librive_harfbuzz.a       __isoc23_strtol __isoc23_strtoul
libluau_vm.a             __isoc23_strtoll __isoc23_strtoul __isoc23_strtoull

$ for f in librive.a librive_native.a librive_pls_renderer.a librive_yoga.a; do
    printf '%-24s %s\n' "$f" "$(strings -a $f | grep -c '_ZSt21ios_base_library_initv')"
  done
librive.a                93
librive_native.a         1
librive_pls_renderer.a   1
librive_yoga.a           1

The shared build shipped in the same archive shows the resulting floor
directly:

$ objdump -p rive_linux/lib/debug_shared/librive_native.so \
    | grep -oE 'GLIBC(XX)?_[0-9][0-9.]*' | sort -Vu | tail -4
GLIBC_2.34
GLIBC_2.35
GLIBC_2.38
GLIBCXX_3.4.32

Why this can't be worked around downstream

Building the application on an older toolchain is precisely what fails —
the references come from the prebuilt .a files that linux/CMakeLists.txt
links from bin/lib/release/, so they are present regardless of the app's own
compiler. -static-libstdc++ would address the GLIBCXX half but not the glibc
symbol versions.

That leaves building rive_native from source (bin/setup.dart --build) in
CI, or dropping Rive on Linux. Both are considerably more costly than a change
to how the artifacts are produced.

Request

Please build the Linux rive_native artifacts against an older sysroot.
manylinux_2_28 (glibc 2.28) is the usual baseline for redistributable native
SDKs and would cover every distribution in the table above; even glibc 2.31
(Ubuntu 20.04) would resolve all of the failing cases.

Happy to test a candidate build against RHEL 9 and Ubuntu 22.04 if useful.

Environment

• rive 0.14.8, rive_native 0.1.8 (artifacts 0.1.8+1)
• Flutter 3.44.8, Linux x86_64 desktop release build
• Build host: GitHub Actions ubuntu-22.04; also reproduced as a runtime
  failure on Rocky Linux 9.8 (glibc 2.34) with artifacts built on 24.04

Possibly related: #613 (whether Linux is officially supported) — the answer
affects how these artifacts should be targeted.

Start with linux/CMakeLists.txt and bin/setup.dart --build, then inspect the Linux artifact packaging path for rive_native. Reproduce the symbol and version checks against the 0.1.8+1 artifacts and identify the build sysroot or toolchain. Done means regenerated Linux artifacts link on Ubuntu 22.04 without requiring GLIBC_2.38 or GLIBCXX_3.4.32.