w32pthreads: Mark functions in compatibility wrapper as av_unused

This avoids annoying warnings about unused functions. The compatibility
wrapper is designed to provide a complete (stub) API, so some functions
being unused by some files is natural and no reason for a warning.

compat/w32pthreads.h

@@ -39,6 +39,7 @@
 #include <windows.h>
 #include <process.h>
 
+#include "libavutil/attributes.h"
 #include "libavutil/internal.h"
 #include "libavutil/mem.h"
 
@@ -86,15 +87,15 @@ static BOOL (WINAPI *cond_wait)(pthread_cond_t *cond, pthread_mutex_t *mutex,
 #define WaitForSingleObject(a, b) WaitForSingleObjectEx(a, b, FALSE)
 #endif
 
-static unsigned __stdcall attribute_align_arg win32thread_worker(void *arg)
+static av_unused unsigned __stdcall attribute_align_arg win32thread_worker(void *arg)
 {
     pthread_t *h = arg;
     h->ret = h->func(h->arg);
     return 0;
 }
 
-static int pthread_create(pthread_t *thread, const void *unused_attr,
-                          void *(*start_routine)(void*), void *arg)
+static av_unused int pthread_create(pthread_t *thread, const void *unused_attr,
+                                    void *(*start_routine)(void*), void *arg)
 {
     thread->func   = start_routine;
     thread->arg    = arg;
@@ -103,7 +104,7 @@ static int pthread_create(pthread_t *thread, const void *unused_attr,
     return !thread->handle;
 }
 
-static void pthread_join(pthread_t thread, void **value_ptr)
+static av_unused void pthread_join(pthread_t thread, void **value_ptr)
 {
     DWORD ret = WaitForSingleObject(thread.handle, INFINITE);
     if (ret != WAIT_OBJECT_0)
@@ -145,7 +146,7 @@ typedef struct  win32_cond_t {
     volatile int is_broadcast;
 } win32_cond_t;
 
-static void pthread_cond_init(pthread_cond_t *cond, const void *unused_attr)
+static av_unused void pthread_cond_init(pthread_cond_t *cond, const void *unused_attr)
 {
     win32_cond_t *win32_cond = NULL;
     if (cond_init) {
@@ -169,7 +170,7 @@ static void pthread_cond_init(pthread_cond_t *cond, const void *unused_attr)
     pthread_mutex_init(&win32_cond->mtx_broadcast, NULL);
 }
 
-static void pthread_cond_destroy(pthread_cond_t *cond)
+static av_unused void pthread_cond_destroy(pthread_cond_t *cond)
 {
     win32_cond_t *win32_cond = cond->ptr;
     /* native condition variables do not destroy */
@@ -185,7 +186,7 @@ static void pthread_cond_destroy(pthread_cond_t *cond)
     cond->ptr = NULL;
 }
 
-static void pthread_cond_broadcast(pthread_cond_t *cond)
+static av_unused void pthread_cond_broadcast(pthread_cond_t *cond)
 {
     win32_cond_t *win32_cond = cond->ptr;
     int have_waiter;
@@ -216,7 +217,7 @@ static void pthread_cond_broadcast(pthread_cond_t *cond)
     pthread_mutex_unlock(&win32_cond->mtx_broadcast);
 }
 
-static int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
+static av_unused int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
 {
     win32_cond_t *win32_cond = cond->ptr;
     int last_waiter;
@@ -248,7 +249,7 @@ static int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
     return pthread_mutex_lock(mutex);
 }
 
-static void pthread_cond_signal(pthread_cond_t *cond)
+static av_unused void pthread_cond_signal(pthread_cond_t *cond)
 {
     win32_cond_t *win32_cond = cond->ptr;
     int have_waiter;
@@ -273,7 +274,7 @@ static void pthread_cond_signal(pthread_cond_t *cond)
     pthread_mutex_unlock(&win32_cond->mtx_broadcast);
 }
 
-static void w32thread_init(void)
+static av_unused void w32thread_init(void)
 {
 #if _WIN32_WINNT < 0x0600
     HANDLE kernel_dll = GetModuleHandle(TEXT("kernel32.dll"));