This seems to violate C11 standard (see https://en.cppreference.com/w/c/thread), which says "If the macro constant __STDC_NO_THREADS__(C11) is defined by the compiler, the header <threads.h> and all of the names listed here are not provided." and leads to various issues such as https://github.com/numpy/numpy/issues/18179
The clang/llvm project appears to deal with this on per platform basis. I am not sure whether this is an OpenBSD bug, or the upstream Clang bug, though. Dima
