The standard library makelib package implements top-level Mythryl make / compile functionality.
The makelib package implements the Makelib API.
The makelib package source code is in src/lib/core/makelib/makelib.pkg, which is a wrapper for src/lib/core/internal/makelib-internal.pkg; the interesting code is in the makelib_g definition in src/app/makelib/main/makelib-g.pkg.
The above information is manually maintained and may contain errors.
Makelib