Windows loader is part of the system ABI, and programs' libc(s) are loaded by it.

One of the ways Windows manages to support multiple libc's is by being careful not to mix allocators; if a system API you call allocates on your behalf, your libc can't free it, the system API will offer a function to free it.

Windows loader is certainly available to user programs though; LoadLibrary has been around longer than many developers.