autoconf can actually handle #define HAVE_FOO 0 as the default

Change-Id: I6cd70d885a3fe3ab53f7523d1a5da6ae30ee01e3

config_host/README

@@ -20,11 +20,7 @@ Adding a new setting:
         - add AC_CONFIG_HEADERS([config_host/config_XXX.h]) next to the others
             in configure.ac
         - add config_XXX.h to config_host/.gitignore
-- add #undef HAVE_FOO to the config_host/config_XXX.h , possibly with a comment
-- if the setting is an on/off setting (i.e. not a value of anything),
-  add the following block right after it
-#ifndef HAVE_FOO
-#define HAVE_FOO 0
-#endif
+- add #define HAVE_FOO 0 to the config_host/config_XXX.h , possibly with a comment
+  (do not use #undef HAVE_FOO, unless the setting has more values than on/off)
 - add #include <config_XXX.h> before any #if HAVE_FOO in a source file
-- make sure you use #if HAVE_FOO, do not use #ifdef
+- make sure you use #if HAVE_FOO for on/off settings, do not use #ifdef

config_host/config_global.h.in

@@ -12,42 +12,14 @@ Any change in this header will cause a rebuild of almost everything.
 #ifndef CONFIG_GLOBAL_H
 #define CONFIG_GLOBAL_H
 
-#undef HAVE_CXX11_DELETE
-#ifndef HAVE_CXX11_DELETE
 #define HAVE_CXX11_DELETE 0
-#endif
-
-#undef HAVE_CXX11_OVERRIDE
-#ifndef HAVE_CXX11_OVERRIDE
 #define HAVE_CXX11_OVERRIDE 0
-#endif
-
-#undef HAVE_CXX11_PERFECT_FORWARDING
-#ifndef HAVE_CXX11_PERFECT_FORWARDING
 #define HAVE_CXX11_PERFECT_FORWARDING 0
-#endif
-
-#undef HAVE_GCC_BUILTIN_ATOMIC
-#ifndef HAVE_GCC_BUILTIN_ATOMIC
 #define HAVE_GCC_BUILTIN_ATOMIC 0
-#endif
-
 #define HAVE_GCC_PRAGMA_DIAGNOSTIC_MODIFY 0
 #define HAVE_GCC_PRAGMA_DIAGNOSTIC_SCOPE 0
-
-#undef HAVE_SFINAE_ANONYMOUS_BROKEN
-#ifndef HAVE_SFINAE_ANONYMOUS_BROKEN
 #define HAVE_SFINAE_ANONYMOUS_BROKEN 0
-#endif
-
-#undef HAVE_THREADSAFE_STATICS
-#ifndef HAVE_THREADSAFE_STATICS
 #define HAVE_THREADSAFE_STATICS 0
-#endif
-
-#undef HAVE_SYSLOG_H
-#ifndef HAVE_SYSLOG_H
 #define HAVE_SYSLOG_H 0
-#endif
 
 #endif

config_host/config_graphite.h.in

 #ifndef CONFIG_GRAPHITE_H
 #define CONFIG_GRAPHITE_H
 
-#undef ENABLE_GRAPHITE
-#ifndef ENABLE_GRAPHITE
 #define ENABLE_GRAPHITE 0
-#endif
 
 #endif

config_host/config_kde4.h.in

@@ -5,9 +5,6 @@ Settings for KDE4 integration.
 #ifndef CONFIG_KDE4_H
 #define CONFIG_KDE4_H
 
-#undef KDE_HAVE_GLIB
-#ifndef KDE_HAVE_GLIB
 #define KDE_HAVE_GLIB 0
-#endif
 
 #endif

config_host/config_mingw.h.in

 #ifndef CONFIG_MINGW
 #define CONFIG_MINGW
 
-#undef HAVE_FMERGENEUTRALITEMS
-#ifndef HAVE_FMERGENEUTRALITEMS
 #define HAVE_FMERGENEUTRALITEMS 0
-#endif
 
 #endif

config_host/config_telepathy.h.in

 #ifndef CONFIG_TELEPATHY
 #define CONFIG_TELEPATHY
 
-#undef ENABLE_TELEPATHY
-#ifndef ENABLE_TELEPATHY
 #define ENABLE_TELEPATHY 0
-#endif
 
 #endif

config_host/config_vclplug.h.in

@@ -7,24 +7,9 @@ Settings about which X11 desktops have support enabled.
 #ifndef CONFIG_VCLPLUG_H
 #define CONFIG_VCLPLUG_H
 
-#undef ENABLE_GTK
-#ifndef ENABLE_GTK
 #define ENABLE_GTK 0
-#endif
-
-#undef ENABLE_KDE
-#ifndef ENABLE_KDE
 #define ENABLE_KDE 0
-#endif
-
-#undef ENABLE_KDE4
-#ifndef ENABLE_KDE4
 #define ENABLE_KDE4 0
-#endif
-
-#undef ENABLE_TDE
-#ifndef ENABLE_TDE
 #define ENABLE_TDE 0
-#endif
 
 #endif