There is a __used member in glibc's posix_spawn_file_actions_t in spawn.h, so we must temporarily undefine __used when including it, otherwise Support/Unix/Program.inc fails to build. This is based on similar handling for __unused in other headers. Fixes: 31ba4ce8898f ("Allow bootstrapping llvm-tblgen on macOS and Linux") MFC after: 1 week