[CMake] TEST_BIG_ENDIAN fails for a CXX project

[gryan at akoostix.com]

Hi! I have a project specified as CXX explicitly, and it requires knowing
the endian of the machine. I can't seem to use the TEST_BIG_ENDIAN module,
because it's a .c compilation and I get a

... /CheckIncludeFile.c".  TRY_COMPILE only works for enabled languages.
Currently enabled languages are: CXX
See PROJECT command for help enabling other languages.

Error.

Am I doing something wrong, or is that by design somehow? I can always
just let CMake determine the project type itself, but it seems like there
should be a way to do an endian check for a CXX project.

Thanks!
George