Add cond_wait_timeout()

Add a "timed out" version of cond_wait().

app/src/lock_util.h

@@ -1,6 +1,8 @@
 #ifndef LOCKUTIL_H
 #define LOCKUTIL_H
 
+#include <stdint.h>
+
 // forward declarations
 typedef struct SDL_mutex SDL_mutex;
 typedef struct SDL_cond SDL_cond;
@@ -14,6 +16,10 @@ mutex_unlock(SDL_mutex *mutex);
 void
 cond_wait(SDL_cond *cond, SDL_mutex *mutex);
 
+// return 0 or SDL_MUTEX_TIMEDOUT
+int
+cond_wait_timeout(SDL_cond *cond, SDL_mutex *mutex, uint32_t ms);
+
 void
 cond_signal(SDL_cond *cond);