fix cmake MESSAGE_ONCE macro for multi-line messages

Author: vuvova

cmake/misc.cmake

@@ -1,6 +1,13 @@
-FUNCTION(MESSAGE_ONCE id out)
-  IF(NOT __msg1_${id} STREQUAL "${out}")
+IF ("${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION}.${CMAKE_PATCH_VERSION}" VERSION_LESS "2.8.7")
+  FUNCTION(MESSAGE_ONCE id out)
     MESSAGE(STATUS "${out}")
-  ENDIF()
-  SET(__msg1_${id} "${out}" CACHE INTERNAL "")
-ENDFUNCTION()
+  ENDFUNCTION()
+ELSE()
+  FUNCTION(MESSAGE_ONCE id out)
+    STRING(MD5 hash "${out}")
+    IF(NOT __msg1_${id} STREQUAL "${hash}")
+      MESSAGE(STATUS "${out}")
+    ENDIF()
+    SET(__msg1_${id} ${hash} CACHE INTERNAL "")
+  ENDFUNCTION()
+ENDIF()