debian/rules: Make compiler warnings non-fatal

Explicitly set --disable-Werror to make the build succeed even if warnings are
emitted.

This avoid issues like new versions of the compiler introducing new warnings
and thus breaking the build even if no regression was introduced.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

debian/rules

@@ -11,6 +11,7 @@ include /usr/share/dpkg/default.mk
 override_dh_auto_configure:
 	dh_auto_configure \
 		-- \
+		--disable-Werror \
 		--with-systemdsystemunitdir=/lib/systemd/system \
 		--enable-always-build-tests \
 		--enable-installed-tests \