Consider removing dependency on gcompat

[jxyang]

gcompat provides a compatibility layer between musl and glibc, but unfortunately the work is far from complete. And it seems the repo is not actively maintained. https://git.adelielinux.org/adelie/gcompat. This repo is fairly unstable and frequently goes offline. I had to create a mirror at https://github.com/jxyang/gcompat for the Mystikos pipelines.

We should evaluate how many glibc functions that are patched in gcompat but not in MUSL. From there we should consider moving them to our own glibc compatibility layer. My wild guess is that the number should be < 30.