Clean up some kati warnings

Kati has a `--warn` option that adds some extra Kati-specific warnings
-- like using undefined make functions, undefined user functions, likely
bad variable lookups, etc. Some of these are bugs, others are fine doing
nothing. This fixes up all of them in the core build system.

It also complains about $(eval) usage in a recipe not being recommended.
Those aren't handled as part of this change.

Bug: 72661763
Test: build-aosp_arm.ninja is identical before and after
Change-Id: I8e00af142a7745236d3ad4efc9e91ec3ce71a511