[clang] [RFC][clang][BPF] Make trivial uninit var value to be 0 (PR #125601)

[via cfe-commits]

4ast wrote:

I agree with Eduard. I think we should abandon this patch and make -fsanitize=undefined work.
undef can be mapped to a new bpf_fastcall kfunc no args and void return, so no extra register pressure and call can be inserted. That kfunc can eventually abort prog execution and print into upcoming per-prog trace_pipe
(which we're adding to support deadlock reports, and aborts on page faults)

https://github.com/llvm/llvm-project/pull/125601