fix configure warnings when checking dbus/dbus.h and ibus-1.0/ibus.h .. by adding DBUS_CFLAGS and IBUS_CFLAGS to CPPFLAGS: configure: WARNING: dbus/dbus.h: accepted by the compiler, rejected by the preprocessor! configure: WARNING: dbus/dbus.h: proceeding with the compiler's result configure: WARNING: ibus-1.0/ibus.h: accepted by the compiler, rejected by the preprocessor! configure: WARNING: ibus-1.0/ibus.h: proceeding with the compiler's result