mimallloc/src/prim/readme.md

This is the portability layer where all primitives needed from the OS are defined.

• prim.h: API definition
• prim.c: Selects one of prim-unix.c, prim-wasi.c, or prim-windows.c depending on the host platform.

Note: still work in progress, there may be other places in the sources that still depend on OS ifdef's.