[PATCH] Disable use of std::call_once on OpenBSD with libstdc++

[Joerg Sonnenberger via llvm-commits]

On Sat, Oct 15, 2016 at 04:46:19PM -0400, Brad Smith via llvm-commits wrote:
> Disable the use of std::call_once on OpenBSD with libstc++. It was noticed this caused
> performance regressions and deadlocks.

I'd prefer to reorder this somewhat to make it clear what is tested:

LLVM_ON_UNIX && (LIBCPP_VERSION || !(NetBSD || OpenBSD || ppc)).

and invert the comment accordingly, e.g. "std::call_once from libc++ is
used on all Unix platforms. Other implementations like libstdc++ are
known to have problems on NetBSD, OpenBSD and PowerPC."

This is a change on PPC, but it seems to match the intention.

Joerg