debian/rules: Enable -Wl,--as-needed.

debian/rules

 #!/usr/bin/make -f
-#DH_VERBOSE = 1
+# -*- makefile -*-
+# Uncomment this to turn on verbose mode.
+# export DH_VERBOSE=1
+
+# see FEATURE AREAS in dpkg-buildflags(1)
 export DEB_BUILD_MAINT_OPTIONS = hardening=+all
+export DEB_LDFLAGS_MAINT_APPEND = -Wl,--as-needed
+
 
 %:
 	dh [email protected]