This is the portability layer where all primitives needed from the OS are defined.
include/mimalloc/prim.h: primitive portability API definition.
prim.c: Selects one of unix/prim.c, wasi/prim.c, or windows/prim.c depending on the host platform (and on macOS, osx/prim.c defers to unix/prim.c).
include/mimalloc/prim-tls.h: primitive TLS model (thread local, pthreads, etc)
prim-tls.c: TLS model implementation
Note: still work in progress, there may still be places in the sources that still depend on OS ifdef's.