* Don't define `_POSIX_THREADS` unless threads are enabled.
Fixes #355.
* Remove `_POSIX_THREADS` from predefined-macros.txt.
#define _POSIX_STREAM_MAX 8
#define _POSIX_SYMLINK_MAX 255
#define _POSIX_SYMLOOP_MAX 8
-#define _POSIX_THREADS _POSIX_VERSION
#define _POSIX_THREAD_ATTR_STACKADDR _POSIX_VERSION
#define _POSIX_THREAD_ATTR_STACKSIZE _POSIX_VERSION
#define _POSIX_THREAD_CPUTIME _POSIX_VERSION
#endif
#define _POSIX_VDISABLE 0
+#if defined(__wasilibc_unmodified_upstream) || defined(_REENTRANT)
#define _POSIX_THREADS _POSIX_VERSION
+#endif
#define _POSIX_THREAD_PROCESS_SHARED _POSIX_VERSION
#define _POSIX_THREAD_SAFE_FUNCTIONS _POSIX_VERSION
#define _POSIX_THREAD_ATTR_STACKADDR _POSIX_VERSION