Fix failure to build from source with modern _host_ glibc/gcc.

One should not define __USE_GNU directly, and instead _GNU_SOURCE
should be defined as early as possible, before first (indirect)
inclusion of features.h

Change-Id: I4d109d4fa0c3d266b873d2a0a66a52e1a4faa234
Signed-off-by: Dmitrijs Ledkovs <dmitrijs.ledkovs@canonical.com>
Merge branch 'cm-10.1' of git://github.com/CyanogenMod/android_system_core into jb-mv

Conflicts:
	libcorkscrew/arch-x86/backtrace-x86.c

Change-Id: I76d062878dd658f80579a2d1facedf9cbd122627