Backport of 607e57c6c62c009 for 5.10 and 5.15

Hi Greg and Sasha,

Please find attached backports for commit 607e57c6c62c ("hardening: Remove Clang's enable flag for -ftrivial-auto-var-init=zero") along with prerequisite changes for 5.10 and 5.15. This change is necessary to keep CONFIG_INIT_STACK_ALL_ZERO working with clang-16. This change is already queued up for 5.19 and newer and it is not relevant for 5.4 and older (at least upstream, I'll be doing backports for older Android branches shortly). If there are any questions or problems, please let me know!

Cheers, Nathan