Only define an "uninstall" target if it's not already defined (e.g. by projects that include json-c)

CMakeLists.txt

@@ -436,10 +436,12 @@ include_directories(${PROJECT_BINARY_DIR})
 add_subdirectory(doc)
 
 # uninstall
-add_custom_target(uninstall
-  COMMAND cat ${PROJECT_BINARY_DIR}/install_manifest.txt | xargs rm
-  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
-)
+if(NOT TARGET uninstall)
+	add_custom_target(uninstall
+	  COMMAND cat ${PROJECT_BINARY_DIR}/install_manifest.txt | xargs rm
+	  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+	)
+endif()
 
 # XXX for a normal full distribution we'll need to figure out
 # XXX how to build both shared and static libraries.