[compiler-rt] [libcxxabi] [libunwind] [PAC][libunwind] Fix gcc build of libunwind and compiler-rt (PR #164535)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> > Hmm, the unwind docs claim gcc 4.7 or clang 3.5 which seems optimistic?
> 
> Yeah, exactly. I would be _very_ surprised if that was actually true.

Well contrary to libcxxabi and libcxx, libunwind doesn't really do much advanced that requires specific compiler features (other than new additions like PAC stuff), so it wouldn't surprise me if it essentially worked fine, potentially modulo one or two trivial details or so.

https://github.com/llvm/llvm-project/pull/164535