systemd: fix endian detection for powerpc

Fixes http://autobuild.buildroot.net/results/d53/d5305af6e47da7a577e391c96328ca952c149cd1/



Apply two patches from upstream git to fix powerpc endian detection. These patches
are already part of systemd v216, so they should be dropped when the package
is bumped.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>