[libxml++] configure.ac: Use -Wsuggest-override with --enable-warnings=fatal

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 74475f3dde1c4efe764d79d1118cd00c48faa36a
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Mon Nov 16 16:37:11 2015 +0100

    configure.ac: Use -Wsuggest-override with --enable-warnings=fatal

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 561949a..a24a9b7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -49,7 +49,7 @@ MM_ARG_WITH_TAGFILE_DOC([glibmm-2.4.tag], [glibmm-2.4])
 # Evaluate the --enable-warnings=level option.
 MM_ARG_ENABLE_WARNINGS([LIBXMLXX_WXXFLAGS],
         [-Wall],
-        [-pedantic -Wall -Wextra -Wformat-security -Wshadow -Wno-long-long],
+        [-pedantic -Wall -Wextra -Wformat-security -Wsuggest-override -Wshadow -Wno-long-long],
         [G GLIBMM SIGCXX])
 
 # Offer the ability to omit some API from the library.