Wrap SDL thread functions into scrcpy-specific API

The goal is to expose a consistent API for system tools, and paves the
way to make the "core" independant of SDL in the future.

app/src/util/thread.h

@@ -0,0 +1,66 @@
+#ifndef SC_THREAD_H
+#define SC_THREAD_H
+
+#include "common.h"
+
+#include <stdbool.h>
+#include <stdint.h>
+
+/* Forward declarations */
+typedef struct SDL_Thread SDL_Thread;
+typedef struct SDL_mutex SDL_mutex;
+typedef struct SDL_cond SDL_cond;
+
+typedef int sc_thread_fn(void *);
+
+typedef struct sc_thread {
+    SDL_Thread *thread;
+} sc_thread;
+
+typedef struct sc_mutex {
+    SDL_mutex *mutex;
+} sc_mutex;
+
+typedef struct sc_cond {
+    SDL_cond *cond;
+} sc_cond;
+
+bool
+sc_thread_create(sc_thread *thread, sc_thread_fn fn, const char *name,
+                 void *userdata);
+
+void
+sc_thread_join(sc_thread *thread, int *status);
+
+bool
+sc_mutex_init(sc_mutex *mutex);
+
+void
+sc_mutex_destroy(sc_mutex *mutex);
+
+void
+sc_mutex_lock(sc_mutex *mutex);
+
+void
+sc_mutex_unlock(sc_mutex *mutex);
+
+bool
+sc_cond_init(sc_cond *cond);
+
+void
+sc_cond_destroy(sc_cond *cond);
+
+void
+sc_cond_wait(sc_cond *cond, sc_mutex *mutex);
+
+// return true on signaled, false on timeout
+bool
+sc_cond_timedwait(sc_cond *cond, sc_mutex *mutex, uint32_t ms);
+
+void
+sc_cond_signal(sc_cond *cond);
+
+void
+sc_cond_broadcast(sc_cond *cond);
+
+#endif