MFC 286370:
Add various tests to ensure that invalid arguments passed to mmap()
trigger failures.

Note: most of the tests that should provoke an EINVAL error do not
pass on stable/10 as stable/10 does not have the changes that added
more strict parameter checking to mmap(). Those changes will not be
merged to stable/10, so I have disabled them via #if 0 with a comment
explaining why.