build: unify and fix endian tests

build: unify and fix endian tests

Unify the endian tests out of lib/ccan/wscript into wafsamba since
they're almost cross-compile friendly.
While at it fix them to be so by moving the preprocessor directives out
of main scope since that will fail.
And keep the WORDS_BIGENDIAN, HAVE_LITTLE_ENDIAN and HAVE_BIG_ENDIAN
defines separate because of different codebases.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: David Disseldorp <ddiss@samba.org>