This way it's a lot harder for us to screw up (since we should always
be including <sys/cdefs.h> anyway).
Bug: 14659579
Change-Id: I23070fff3296b0d1c683bb5e3a6e214146327d53
<features.h> is supposed to take user-settable stuff like _GNU_SOURCE
and _BSD_SOURCE and turn them into __USE_GNU and __USE_BSD for use in
the C library headers. Instead, bionic used to unconditionally define
_BSD_SOURCE and _GNU_SOURCE, and then test _GNU_SOURCE in the header
files (which makes no sense whatsoever).
Bug: 14659579
Change-Id: Ice4cf21a364ea2e559071dc8329e995277d5b987
