diff '--color=auto' -ur protobuf-c-1.5.2.orig/configure.ac protobuf-c-1.5.2/configure.ac
--- protobuf-c-1.5.2.orig/configure.ac	2025-04-07 03:17:27.000000000 +0200
+++ protobuf-c-1.5.2/configure.ac	2026-05-30 16:21:15.822038984 +0200
@@ -69,7 +69,7 @@
   AS_HELP_STRING([--disable-protoc], [Disable building protoc_c (also disables tests)]))
 if test "x$enable_protoc" != "xno"; then
   AC_LANG_PUSH([C++])
-  AX_CXX_COMPILE_STDCXX(17, noext, mandatory)
+  dnl AX_CXX_COMPILE_STDCXX(20, noext, mandatory)
   PKG_CHECK_MODULES([protobuf], [protobuf >= 3.0.0])
 
   save_CPPFLAGS="$CPPFLAGS"