auto remove empty /usr/share dir

Often times, the only reason /usr/share exists is because of documentation
installed into it.  So once we're done cleaning the docs, attempt to rmdir
/usr/share.  If it's empty, things will work out nicely.

[Peter: use make infrastructure to ignore errors rather than shell]
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

Makefile

@@ -416,6 +416,7 @@ ifneq ($(BR2_HAVE_DOCUMENTATION),y)
 	rm -rf $(TARGET_DIR)/usr/info $(TARGET_DIR)/usr/share/info
 	rm -rf $(TARGET_DIR)/usr/doc $(TARGET_DIR)/usr/share/doc
 	rm -rf $(TARGET_DIR)/usr/share/gtk-doc
+	-rmdir $(TARGET_DIR)/usr/share 2>/dev/null
 endif
 	find $(TARGET_DIR) -type f -perm +111 | xargs $(STRIPCMD) 2>/dev/null || true
 	find $(TARGET_DIR)/lib/modules -type f -name '*.ko' | \