POSIX says ftw/nftw "shall fail" in various cases where BSD's fts_open
doesn't. Since our ftw/nftw are written in terms of fts_open, add a back
door so we can hint to ourselves when we should have the POSIX semantics.
Also pull several O_CLOEXEC and don't-null-check-before-free cleanups
from upstream, and add a couple of tests.
Bug: http://b/31152735
Test: ran bionic tests and LTP "nftw01" test
Change-Id: Ib05facacc1da4c8b2ab48e9ecce88f11a5406630
SELinux denies access to some files in /sys, so we can't just trawl
through that asserting general truths. Instead, create a small known
tree.
Sadly neither ftw nor nftw takes user callback data, otherwise it would
be nice to assert that we visit all the expected nodes.
Bug: 19252748
Change-Id: Ib5309c38aaef53e6030281191a265a8d5a619044
