only define tss_t and functions if we don't have threads.h

p99/p99_tss.h

@@ -21,6 +21,8 @@
 #include "p99_defarg.h"
 #include "p99_atomic.h"
 
+#if !p99_has_feature(threads_h)
+
 /**
  ** @addtogroup threads C11 thread emulation on top of POSIX threads
  **
@@ -180,6 +182,9 @@ int tss_set(tss_t p00_key, void *p00_val) {
   return pthread_setspecific(P99_ENC(p00_key), p00_val) ? thrd_error : thrd_success;
 }
 
+
+#endif
+
 /**
  ** @brief A stub structure to hold a thread local variable if
  ** ::thread_local is not available.