[LyX/master] Do not use -Wfloat-conversion with recent gcc versions

[Jean-Marc]

commit a22f7b7001148057a1563d1a8e4a279bdbb19d0b
Author: Jean-Marc <lasgout...@lyx.org>
Date:   Thu Sep 10 18:12:35 2015 +0200

    Do not use -Wfloat-conversion with recent gcc versions

diff --git a/config/lyxinclude.m4 b/config/lyxinclude.m4
index 3a0a6f3..b488cef 100644
--- a/config/lyxinclude.m4
+++ b/config/lyxinclude.m4
@@ -312,14 +312,7 @@ if test x$GXX = xyes; then
   fi
   dnl Warnings are for preprocessor too
   if test x$enable_warnings = xyes ; then
-      case $gxx_version in
-          4.0*|4.1*|4.2*|4.3*|4.4*|4.5*|4.6*|4.7*|4.8*|clang)
-              AM_CPPFLAGS="$AM_CPPFLAGS -Wall -Wextra"
-              ;;
-          *)
-              AM_CPPFLAGS="$AM_CPPFLAGS -Wall -Wextra -Wfloat-conversion"
-              ;;
-      esac
+      AM_CPPFLAGS="$AM_CPPFLAGS -Wall -Wextra"
   fi
   case $gxx_version in
       2.*|3.*) AC_ERROR([gcc 4.x is required]);;