Fix with nettle >=4

Index: configure
--- configure.orig
+++ configure
@@ -12750,12 +12750,12 @@ fi
 printf "%s\n" "$ac_cv_enable_nettle" >&6; }
 case $ac_cv_enable_nettle in
   yes)
-    ac_fn_c_check_header_compile "$LINENO" "nettle/md5-compat.h" "ac_cv_header_nettle_md5_compat_h" "$ac_includes_default"
+    ac_fn_c_check_header_compile "$LINENO" "nettle/md5.h" "ac_cv_header_nettle_md5_compat_h" "$ac_includes_default"
 if test "x$ac_cv_header_nettle_md5_compat_h" = xyes
 then :
 
 else case e in #(
-  e) as_fn_error $? "nettle/md5-compat.h is needed but not found - you will need to install package 'nettle-dev' or similar. The feature can be disabled with --disable-nettle" "$LINENO" 5 ;;
+  e) as_fn_error $? "nettle/md5.h is needed but not found - you will need to install package 'nettle-dev' or similar. The feature can be disabled with --disable-nettle" "$LINENO" 5 ;;
 esac
 fi
 
