MFC r312110:

Fix -Wsign-compare warnings

The loop index (i) doesn't need to be size_t as its comparison is signed

MFC r298301:

Fix leaks and test for getpagesize() returning == -1

- close file descriptors after use.
- Always munmap memory regions after mmap'ing them.
- Make sure getpagesize() returns a value greater than 0 and use a
cached value instead of always calling getpagesize(3).

CID: 1331374-1331377, 1331653-1331662

MFC 287448:
Add more mmap tests related to character devices.
- Add cdev-related tests for bad args.
- Add two simple tests cases for mapping /dev/zero that test for
MAP_ANON-like behavior.

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.

MFC 286369:
Convert the map_at_zero test case to ATF. In particular, this will
facilitate adding more mmap() tests.

MFC 287448:
Add more mmap tests related to character devices.
- Add cdev-related tests for bad args.
- Add two simple tests cases for mapping /dev/zero that test for
MAP_ANON-like behavior.

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.

MFC 286369:
Convert the map_at_zero test case to ATF. In particular, this will
facilitate adding more mmap() tests.