I am seeing that lots of the fixes proposed by the author are things like "missing import because glibc exposes some symbols by mistake and musl does not". And this is definitely the kind of fix that upstream would accept[2].
It exists. See gcompat.
This is exactly the opposite that I was talking about. What I was talking is a library that expose glibc compatible headers to compile software that uses Glibc-isms with minor or zero modifications, but this instead is a compatibility layer for binaries and doesn't expose headers (probably for proprietary software that can't be recompiled).