minijail: fix Makefile and bpf.h to build in CrOS

Make the following two changes to ensure that minijail builds
in CrOS:

1) Edit references to the previously renamed signal.o file to
   signal_handler.o in the Makefile

2) Add a comparison of __LITTLE_ENDIAN with __BYTE_ORDER to
   bpf.h, since __LITTLE_ENDIAN__ is not defined when building
   for CrOS.

BUG: 24680644
Change-Id: I152573d29a87a3a685c0d27e728632e84462e8ef
TEST: Cherry-pick change to CrOS and minijail build succeeds.
2 files changed