fix: only add uninstall target if not previously defined

CMakeLists.txt

@@ -66,9 +66,12 @@ configure_file("${CMAKE_CURRENT_SOURCE_DIR}/assimp-config.cmake.in" "${CMAKE_CUR
 configure_file("${CMAKE_CURRENT_SOURCE_DIR}/assimp-config-version.cmake.in" "${CMAKE_CURRENT_BINARY_DIR}/assimp-config-version.cmake" @ONLY IMMEDIATE)
 install(FILES "${CMAKE_CURRENT_BINARY_DIR}/assimp-config.cmake" "${CMAKE_CURRENT_BINARY_DIR}/assimp-config-version.cmake" DESTINATION "${ASSIMP_LIB_INSTALL_DIR}/cmake/assimp-${ASSIMP_VERSION_MAJOR}.${ASSIMP_VERSION_MINOR}" COMPONENT ${LIBASSIMP-DEV_COMPONENT})
 
-# add make uninstall capability
-configure_file("${CMAKE_CURRENT_SOURCE_DIR}/cmake-modules/cmake_uninstall.cmake.in" "${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake" IMMEDIATE @ONLY)
-add_custom_target(uninstall "${CMAKE_COMMAND}" -P "${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake")
+# Only generate this target if no higher-level project already has
+IF (NOT TARGET uninstall)
+	# add make uninstall capability
+	configure_file("${CMAKE_CURRENT_SOURCE_DIR}/cmake-modules/cmake_uninstall.cmake.in" "${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake" IMMEDIATE @ONLY)
+	add_custom_target(uninstall "${CMAKE_COMMAND}" -P "${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake")
+ENDIF()
 
 # Globally enbale Boost resp. the Boost workaround – it is also needed by the
 # tools which include the Assimp headers.