Because of this:
https://github.com/emscripten-core/emscripten/blob/main/system/lib/libc/musl/src/conf/confstr.c?plain=1#L21
I have a PR to weak link confstr so we can replace it:
emscripten-core/emscripten#25040

In the meantime, we can just check for Emscripten in platform.libc_ver().

Linked PRs

• gh-138130: Fix return value of libc_ver() on Emscripten #138132
• [3.14] gh-138130: Fix return value of libc_ver() on Emscripten (GH-138132) #138312