[CMake] avoid tests dir on BUILD_TESTING=OFF

Author: nim65s

CMakeLists.txt

@@ -185,7 +185,9 @@ IF(NOT INSTALL_PYTHON_INTERFACE_ONLY)
 ENDIF(NOT INSTALL_PYTHON_INTERFACE_ONLY)
 
 ADD_SUBDIRECTORY(src)
-ADD_SUBDIRECTORY(tests)
+IF(BUILD_TESTING)
+  ADD_SUBDIRECTORY(tests)
+ENDIF(BUILD_TESTING)
 ADD_SUBDIRECTORY(doc)
 
 PKG_CONFIG_APPEND_LIBS(${PROJECT_NAME})