[LyX/master] Disable warning for deprecated functions in autoconf builds

[Jean-Marc Lasgouttes]

commit a0b9b9b678fececb590ae61d6c369e059836fc79
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Mon Nov 2 15:45:27 2015 +0100

    Disable warning for deprecated functions in autoconf builds
    
    This gets rid in particular of warnings on auto_ptr. This flag should be 
removed when 2.3 development start and we switch to unique_ptr.

diff --git a/config/lyxinclude.m4 b/config/lyxinclude.m4
index ff38dad..30697d7 100644
--- a/config/lyxinclude.m4
+++ b/config/lyxinclude.m4
@@ -298,7 +298,7 @@ if test x$GXX = xyes; then
   fi
   dnl Warnings are for preprocessor too
   if test x$enable_warnings = xyes ; then
-      AM_CPPFLAGS="$AM_CPPFLAGS -Wall -Wextra"
+      AM_CPPFLAGS="$AM_CPPFLAGS -Wall -Wextra -Wno-deprecated-declarations"
   fi
   case $gxx_version in
       2.*|3.*) AC_ERROR([gcc 4.x is required]);;