[clang] [clang][CodeGen] Zero init unspecified fields in initializers in C (#97459) (PR #97121)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for working on this! I'll leave the codegen code review to John and Eli, but I would appreciate explicit documentation in `clang/docs/LanguageExtensions.rst` so that we explicitly document this behavior and users (including the Linux kernel) can rely on it longterm.

https://github.com/llvm/llvm-project/pull/97121