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

Index: configure.ac
--- configure.ac.orig
+++ configure.ac
@@ -76,12 +76,8 @@ AC_ARG_ENABLE([protoc],
 if test "x$enable_protoc" != "xno"; then
   AC_LANG_PUSH([C++])
 
-  AX_CXX_COMPILE_STDCXX(11, noext, mandatory)
-
-  PKG_CHECK_MODULES([protobuf], [protobuf >= 3.0.0],
-    [proto3_supported=yes],
-    [PKG_CHECK_MODULES([protobuf], [protobuf >= 2.6.0])]
-  )
+  AX_CXX_COMPILE_STDCXX(17, noext, mandatory)
+  PKG_CHECK_MODULES([protobuf], [protobuf >= 3.0.0], [proto3_supported=yes])
 
   save_CPPFLAGS="$CPPFLAGS"
   CPPFLAGS="$save_CPPFLAGS $protobuf_CFLAGS"