https://github.com/protobuf-c/protobuf-c/pull/673

Index: build-cmake/CMakeLists.txt
--- build-cmake/CMakeLists.txt.orig
+++ build-cmake/CMakeLists.txt
@@ -88,7 +88,7 @@ if (MSVC AND NOT BUILD_SHARED_LIBS)
 endif (MSVC AND NOT BUILD_SHARED_LIBS)
 
 IF(BUILD_PROTOC)
-SET(CMAKE_CXX_STANDARD 11)
+SET(CMAKE_CXX_STANDARD 17)
 SET(CMAKE_CXX_STANDARD_REQUIRED ON)
 SET(CMAKE_CXX_EXTENSIONS OFF)
 ADD_CUSTOM_COMMAND(OUTPUT protobuf-c/protobuf-c.pb.cc protobuf-c/protobuf-c.pb.h