[clang] [llvm] [RFC][BPF] Do atomic_fetch_*() pattern matching with memory ordering (PR #107343)

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yonghong-song wrote:

Add change in BTFDebug.cpp to ingore dwarf::DW_TAG_atomic_type. Add some info about bpf prog atomic type usage and what skeleton looks like (see commit message in commit 2).

https://github.com/llvm/llvm-project/pull/107343