hadrian: Add dependency from lib/settings to mk/config.mk

In 81975ef3 we attempted to fix #20253 (closed) by adding logic to the bindist Makefile to regenerate the settings file from information gleaned by the bindist configure script. However, this fix had no effect as lib/settings is shipped in the binary distribution (to allow in-place use of the binary distribution). As lib/settings already existed and its rule declared no dependencies, make would fail to use the added rule to regenerate it.

Fix this by explicitly declaring a dependency from lib/settings on mk/config.mk.

Fixes #22982 (closed).