thread: add error if system not supported
@@ -37,6 +37,10 @@ typedef HANDLE thrd_t;
typedef CONDITION_VARIABLE cnd_t;
typedef CRITICAL_SECTION mtx_t;
+#else
+
+#error "thread: system not supported"
+
#endif
enum { mtx_plain = 0, mtx_try = 1, mtx_timed = 2, mtx_recursive = 4 };
