Add check for big endian in backward compatibility scripts

Modules/CMakeBackwardCompatibilityC.cmake

@@ -20,3 +20,6 @@ CHECK_INCLUDE_FILE("limits.h"       CMAKE_HAVE_LIMITS_H)
 CHECK_INCLUDE_FILE("unistd.h"       CMAKE_HAVE_UNISTD_H)
 CHECK_INCLUDE_FILE("sys/prctl.h"    CMAKE_HAVE_SYS_PRCTL_H)
 CHECK_INCLUDE_FILE("pthread.h"      CMAKE_HAVE_PTHREAD_H)
+
+INCLUDE (${CMAKE_ROOT}/Modules/TestBigEndian.cmake)
+TEST_BIG_ENDIAN(CMAKE_WORDS_BIGENDIAN)