[compiler-rt] [rtsan] Support legacy pthread_cond variables (PR #152947)

[via llvm-commits]

https://github.com/davidtrevelyan commented:

No strong objections to merging this from me. If it fixes the issue on @adrew0809's machine and the CI is happy then I think it's low-enough risk to go for it. I do think we should consider whether it would be feasible to get this issue and its solution under meaningful test - if it's not too hard I think it would be wise to do it soon. 

https://github.com/llvm/llvm-project/pull/152947