Replace config-time define HOST_WORDS_BIGENDIAN

Replace config-time define HOST_WORDS_BIGENDIAN

Replace a config-time define with a compile time condition
define (compatible with clang and gcc) that must be declared prior to
its usage. This avoids having a global configure time define, but also
prevents from bad usage, if the config header wasn't included before.

This can help to make some code independent from qemu too.

gcc supports __BYTE_ORDER__ from about 4.6 and clang from 3.2.

Signed-off-by: Marc-André Lureau <[email protected]>
[ For the s390x parts I'm involved in ]
Acked-by: Halil Pasic <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-Id: <20220323155743.1585078[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>