Wayland: avoid accidental export of internal symbols

Some symbols in the generated Wayland code were getting
decorated with WL_EXPORT, causing them to show up in the
libgdk exports. We don't want that.

https://bugzilla.gnome.org/show_bug.cgi?id=710141

gdk/wayland/Makefile.am

@@ -50,6 +50,8 @@ libgdkwaylandinclude_HEADERS = 			\
 
 %-protocol.c : $(srcdir)/protocol/%.xml
 	$(AM_V_GEN)$(WAYLAND_SCANNER) code < $< > $@
+	$(AM_V_GEN)$(SED) -i -e 's/WL_EXPORT //' $@
+
 %-server-protocol.h : $(srcdir)/protocol/%.xml
 	$(AM_V_GEN)$(WAYLAND_SCANNER) server-header < $< > $@
 %-client-protocol.h : $(srcdir)/protocol/%.xml