$NetBSD: patch-configure,v 1.2 2021/01/15 14:33:52 mef Exp $

Let's not force C++20 when the libxml++ dependency can't deal with it.

--- configure.orig	2021-01-15 23:14:58.236623702 +0900
+++ configure	2021-01-15 23:22:01.601329062 +0900
@@ -19482,15 +19482,15 @@ ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS 
 ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
 ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
 
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C++ compiler accepts -std=c++20" >&5
-printf %s "checking whether C++ compiler accepts -std=c++20... " >&6; }
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C++ compiler accepts -std=c++14" >&5
+printf %s "checking whether C++ compiler accepts -std=c++14... " >&6; }
 if test ${ax_cv_check_cxxflags___std_cpp20+y}
 then :
   printf %s "(cached) " >&6
 else $as_nop
 
   ax_check_save_flags=$CXXFLAGS
-  CXXFLAGS="$CXXFLAGS  -std=c++20"
+  CXXFLAGS="$CXXFLAGS  -std=c++14"
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -19515,7 +19515,7 @@ fi
 printf "%s\n" "$ax_cv_check_cxxflags___std_cpp20" >&6; }
 if test x"$ax_cv_check_cxxflags___std_cpp20" = xyes
 then :
-  CXXFLAGS="$CXXFLAGS -std=c++20"
+  CXXFLAGS="$CXXFLAGS -std=c++14"
 else $as_nop
 
  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C++ compiler accepts -std=c++2a" >&5
@@ -19554,15 +19554,15 @@ then :
   CXXFLAGS="$CXXFLAGS -std=c++2a"
 else $as_nop
 
-  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C++ compiler accepts -std=c++17" >&5
-printf %s "checking whether C++ compiler accepts -std=c++17... " >&6; }
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C++ compiler accepts -std=c++14" >&5
+printf %s "checking whether C++ compiler accepts -std=c++14... " >&6; }
 if test ${ax_cv_check_cxxflags___std_cpp17+y}
 then :
   printf %s "(cached) " >&6
 else $as_nop
 
   ax_check_save_flags=$CXXFLAGS
-  CXXFLAGS="$CXXFLAGS  -std=c++17"
+  CXXFLAGS="$CXXFLAGS  -std=c++14"
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -19587,7 +19587,7 @@ fi
 printf "%s\n" "$ax_cv_check_cxxflags___std_cpp17" >&6; }
 if test x"$ax_cv_check_cxxflags___std_cpp17" = xyes
 then :
-  CXXFLAGS="$CXXFLAGS -std=c++17"
+  CXXFLAGS="$CXXFLAGS -std=c++14"
 else $as_nop
 
    { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C++ compiler accepts -std=c++1z" >&5
@@ -19623,7 +19623,7 @@ fi
 printf "%s\n" "$ax_cv_check_cxxflags___std_cpp1z" >&6; }
 if test x"$ax_cv_check_cxxflags___std_cpp1z" = xyes
 then :
-  CXXFLAGS="$CXXFLAGS -std=c++1z"
+  CXXFLAGS="$CXXFLAGS -std=c++14"
 else $as_nop
 
     { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C++ compiler accepts -std=c++14" >&5