Fix detection of directfb.h

- AC_CHECK_HEADER wants CPPFLAGS

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%404390

configure.in

@@ -1323,10 +1323,10 @@ AC_HELP_STRING([--enable-video-directfb], [use DirectFB video driver [[default=n
         fi
         if test x$video_directfb = xyes; then
             # SuSE 11.1 installs directfb-config without directfb-devel
-            save_CFLAGS="$CFLAGS"
-            CFLAGS="$CFLAGS $DIRECTFB_CFLAGS"
+            save_CPPFLAGS="$CPPFLAGS"
+            CPPFLAGS="$CPPFLAGS $DIRECTFB_CFLAGS"
             AC_CHECK_HEADER(directfb.h, have_directfb_hdr=yes, have_directfb_hdr=no)
-            CFLAGS="$save_CFLAGS"
+            CPPFLAGS="$save_CPPFLAGS"
             video_directfb=$have_directfb_hdr
         fi
         AC_MSG_CHECKING(for DirectFB $DIRECTFB_REQUIRED_VERSION support)