Propagate target OS from configure to Makefile

Propagate target OS from configure to Makefile (CONFIG_TARGET_OS) to avoid
duplicating the check in Makefile.  Also allow CROSS_COMPILE for the toolchain
prefix, which is common (e.g. Linux).

Signed-off-by: Aaron Carroll <aaronc@cse.unsw.edu.au>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
configure: compile-time word size detection

Signed-off-by: Aaron Carroll <aaronc@cse.unsw.edu.au>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
configure: endianness check for cross compile

 - Add a cross compile check: assume yes if we can't run a test binary
 - If cross compiling, revert to a compile-time endianess check. This tries
   a few possible ways to detect big endian, but otherwise assumes little. We
   rely on the run-time check to save us if the build-time check is wrong.

Signed-off-by: Aaron Carroll <aaronc@cse.unsw.edu.au>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Android: remove static Android configuration

Android can now be configured dynamically, so remove the static config.
For this we need to modify the socklen_t check #includes which appear to
be wrong anyway.

Signed-off-by: Aaron Carroll <aaronc@cse.unsw.edu.au>
Signed-off-by: Jens Axboe <axboe@kernel.dk>