make: Clean includes/settings file

Now since this is generated by the build system we should ensure that it
is properly cleaned.

[skip ci]

ghc.mk

@@ -1306,6 +1306,7 @@ CLEAN_FILES += includes/DerivedConstants.h
 CLEAN_FILES += includes/ghcautoconf.h
 CLEAN_FILES += includes/ghcplatform.h
 CLEAN_FILES += includes/ghcversion.h
+CLEAN_FILES += $(includes_SETTINGS)
 CLEAN_FILES += utils/ghc-pkg/Version.hs
 CLEAN_FILES += compiler/prelude/primops.txt
 CLEAN_FILES += $(wildcard compiler/primop*incl)