Start of deflate compress-side code, mostly refactoring and stubs so far.
Switching on fortify was not kind to the pending directory. Fix the actual build break (open(O_CREAT) without permissions).
Don't mount a filesystem over an existing one with the same /dev and /dir.

The OS mostly catches this for block devices, but calling "mount -a" twice
shouldn't overmount tmpfs entries with new tmpfs instances. (This needs a test
suite entry, and the test suite needs a root context to run in...)