Fix Moonshine Linux release link error on older glibc

[JRufer]

Problem

The v0.3.0 release build failed to link on the ubuntu-22.04 runners:

rust-lld: error: undefined symbol: __isoc23_strtol / __isoc23_strtoll / __isoc23_strtoull
  >>> ... in archive libort_sys (onnxruntime static lib)

The prebuilt ONNX Runtime static library (pyke, pulled in by ort + download-binaries) is compiled against glibc ≥ 2.38, which redirects strtol/strtoul/… to __isoc23_* symbols. The release runners are ubuntu-22.04 (glibc 2.35), which has no such symbols, so the static link fails. (Windows builds are unaffected.)

Fix

Add a tiny C shim (src/isoc23_compat.c, compiled by a new build.rs for the moonshine feature on Linux only) that provides the __isoc23_* symbols by forwarding to the classic libc functions. This keeps the binary linkable and runnable on older glibc, preserving the AppImage's low glibc floor — rather than bumping the runners to ubuntu-24.04, which would raise the minimum glibc for all Linux users (excluding e.g. Debian 12 / Ubuntu 22.04).

cc is added as a build-dependency; it's already in the graph (whisper-rs-sys), so it adds nothing to compile.

Verified

• Default build unaffected (build.rs no-ops when the feature is off).
• C shim compiles cleanly under --features moonshine.
• The link resolution itself only reproduces on the CI release runners (the ONNX Runtime static lib downloads there); this PR's merge re-triggers that build.

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https://claude.ai/code/session_01GpXWVxBBJvtRgkdMWasSH6

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