Fix `thread_unix.odin`

core/thread/thread_unix.odin

@@ -38,6 +38,7 @@ Thread_Os_Specific :: struct #align 16 {
 //
 _create :: proc(procedure: Thread_Proc, priority := Thread_Priority.Normal) -> ^Thread {
 	__linux_thread_entry_proc :: proc "c" (t: rawptr) -> rawptr {
+		context = runtime.default_context();
 		t := (^Thread)(t);
 		sync.condition_wait_for(&t.start_gate);
 		sync.condition_destroy(&t.start_gate);