cmake: defined `short_little_endian`, `int_little_endian` macros

cmake: defined `short_little_endian`, `int_little_endian` macros

... so CL_CPU_BIG_ENDIAN_P is set in src/base/cl_sysdep.h both for
autotools and CMake builds.

Note 1.

Checking for endianness of both `short` and `int` is necessary only
for 16-bit systems (where `short` can be 8-bit). I doubt anyone is
going to run CLN on such systems in the 21st century. Nevertheless
CMake does the right thing even for such targets (i.e. it tries to
find a 16-bit integer type and figure out its endianness).

Note 2.

These days (circa 2021) the vast majority of CPU architectures are
little endian, so the problem is mostly irrelevant.