[libunwind] [clang-tools-extra] [clang] [llvm] [libunwind] Replace process_vm_readv with SYS_rt_sigprocmask (PR #74791)

[Jordan R AW via llvm-commits]

ajordanr-google wrote:

I don't have Commit Access (I so rarely actually commit to upstream), and I don't think I have yet the "track record of submitting high quality patches" :)

Can someone else merge this once the checks are green?

https://github.com/llvm/llvm-project/pull/74791