posix: add implementation of mmap(), msync(), and munmap()

Add stubs for mmap(), msync(), and munmap() as required by the
_POSIX_MAPPED_FILES Option and POSIX_MAPPED_FILES and
Option Group of IEEE 1003.1-2017.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>
7 files changed