Fixed endianness check for cmake

Signed-off-by: Markus Engel <engel@sero-systems.de>

build-cmake/CMakeLists.txt

@@ -17,7 +17,9 @@ TEST_BIG_ENDIAN(WORDS_BIGENDIAN)
 SET(PACKAGE_STRING "${PACKAGE_NAME} ${PACKAGE_VERSION}")
 ADD_DEFINITIONS(-DPACKAGE_VERSION="${PACKAGE_VERSION}")
 ADD_DEFINITIONS(-DPACKAGE_STRING="${PACKAGE_STRING}")
-ADD_DEFINITIONS(-DWORDS_BIGENDIAN=${WORDS_BIGENDIAN})
+if (${WORDS_BIGENDIAN})
+	ADD_DEFINITIONS(-DWORDS_BIGENDIAN)
+endif()
 
 if(MSVC)
   # using Visual Studio C++