configure.ac: Set CXXFLAGS during --enable-sanitize

For some unknown reason ld was failing to find some asan symbols until I
enabled asan too in CXXFLAGS.

Change-Id: I695314b284277674dc336b40765313a37d238d6e
diff --git a/configure.ac b/configure.ac
index 69e0775..7288c24 100644
--- a/configure.ac
+++ b/configure.ac
@@ -41,6 +41,7 @@
 if test x"$sanitize" = x"yes"
 then
 	CFLAGS="$CFLAGS -fsanitize=address -fsanitize=undefined"
+	CXXFLAGS="$CXXFLAGS -fsanitize=address -fsanitize=undefined"
 	CPPFLAGS="$CPPFLAGS -fsanitize=address -fsanitize=undefined"
 	LDFLAGS="$LDFLAGS -fsanitize=address -fsanitize=undefined"
 fi
@@ -156,8 +157,10 @@
 STD_DEFINES_AND_INCLUDES="-Wall"
 AC_SUBST(STD_DEFINES_AND_INCLUDES)
 
-AC_MSG_RESULT([CFLAGS="$CFLAGS"])
 AC_MSG_RESULT([CPPFLAGS="$CPPFLAGS"])
+AC_MSG_RESULT([CFLAGS="$CFLAGS"])
+AC_MSG_RESULT([CXXFLAGS="$CXXFLAGS"])
+AC_MSG_RESULT([LDFLAGS="$LDFLAGS"])
 
 AC_OUTPUT(
     osmo-pcu.pc