gh-112027: Don't print mimalloc warning after mmap() call (gh-113372)

gh-112027: Don't print mimalloc warning after mmap() call (gh-113372)

gh-112027: Don't print mimalloc warning after mmap

This changes the warning to a "verbose"-level message in prim.c. The
address passed to mmap is only a hint -- it's normal for mmap() to
sometimes not respect the hint and return a different address.