wayland: Use portable sed syntax in gdk/wayland/Makefile.am

Replace non-portable \<, \>, \+ with \(, \), \{, \} to avoid build
failure on systems not using GNU sed.

https://bugzilla.gnome.org/show_bug.cgi?id=792279

gdk/wayland/Makefile.am

@@ -80,11 +80,11 @@ libgdkwaylandinclude_HEADERS = 			\
 .SECONDEXPANSION:
 
 define protostability
-$(shell echo $1 | sed 's/.*\(\<unstable\>\|\<stable\>\).*/\1/')
+$(shell echo $1 | sed 's/.*-\(\(un\)\{0,1\}stable\)-.*/\1/')
 endef
 
 define protoname
-$(shell echo $1 | sed 's/\([a-z\-]\+\)-[a-z]\+-v[0-9]\+/\1/')
+$(shell echo $1 | sed 's/\([a-z\-]\{1,\}\)-[a-z]\{1,\}-v[0-9]\{1,\}/\1/')
 endef
 
 %-protocol.c : $(WAYLAND_PROTOCOLS_DATADIR)/$$(call protostability,$$*)/$$(call protoname,$$*)/$$*.xml