[gnome-system-monitor] build: Replace -std=c++98 with -std=c++11

[Ting-Wei Lan <lantw src gnome org>]

commit e5d3ac014d7acc73c5f508a937c5656ffa8f08ad
Author: Ting-Wei Lan <lantw src gnome org>
Date:   Sat Aug 1 13:50:04 2015 +0800

    build: Replace -std=c++98 with -std=c++11
    
    Gtkmm requires C++11 now.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=753121

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index f661d69..263a63c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -96,7 +96,7 @@ if test "$GCC" = "yes" -a "$set_more_warnings" != "no"; then
     -Wcast-align -Wsign-compare \
     -std=gnu89 \
     $CFLAGS"
-    CXXFLAGS="-Wall -std=c++98 $CXXFLAGS"
+    CXXFLAGS="-Wall -std=c++11 $CXXFLAGS"
 else
     AC_MSG_RESULT(no)
 fi