[clang] [Clang] Initialize bypassed variables w/ trivial-auto-var-init (PR #181937)

[Justin Stitt via cfe-commits]

JustinStitt wrote:

@efriedma-quic ok with 8b2e9fc we now only have two modes. the third mode outlined by `C 6.2.4p6` can be a different follow-up pr. since i don't need to track object lifetime from top of entry block i've dropped lots of the complexity.

@nickdesaulniers i used the test gen script to regen the tests :) see 8b2e9fc

https://github.com/llvm/llvm-project/pull/181937