Do fixes for Gekko mutexes, implement 3DS mutexes

These lines from RetroArch probably should be removed after this PR is in RetroArch's rcheevos copy.
https://github.com/libretro/RetroArch/blob/228426880babb529fae8f01598a6d34698ad3b18/griffin/griffin.c#L193-L195

src/rc_compat.c

@@ -168,22 +168,47 @@ void rc_mutex_unlock(rc_mutex_t* mutex)
 
 void rc_mutex_init(rc_mutex_t* mutex)
 {
-  LWP_MutexInit(mutex, NULL);
+  /* LWP_MutexInit has the handle passed by reference */
+  /* Other LWP_Mutex* calls have the handle passed by value */
+  LWP_MutexInit(&mutex->handle, 1);
 }
 
 void rc_mutex_destroy(rc_mutex_t* mutex)
 {
-  LWP_MutexDestroy(mutex);
+  LWP_MutexDestroy(mutex->handle);
 }
 
 void rc_mutex_lock(rc_mutex_t* mutex)
 {
-  LWP_MutexLock(mutex);
+  LWP_MutexLock(mutex->handle);
 }
 
 void rc_mutex_unlock(rc_mutex_t* mutex)
 {
-  LWP_MutexUnlock(mutex);
+  LWP_MutexUnlock(mutex->handle);
+}
+
+#elif defined(_3DS)
+
+void rc_mutex_init(rc_mutex_t* mutex)
+{
+  RecursiveLock_Init(mutex);
+}
+
+void rc_mutex_destroy(rc_mutex_t* mutex)
+{
+  /* Nothing to do here */
+  (void)mutex;
+}
+
+void rc_mutex_lock(rc_mutex_t* mutex)
+{
+  RecursiveLock_Lock(mutex);
+}
+
+void rc_mutex_unlock(rc_mutex_t* mutex)
+{
+  RecursiveLock_Unlock(mutex);
 }
 
 #else

src/rc_compat.h

@@ -84,7 +84,7 @@ RC_BEGIN_C_DECLS
  #define rc_mutex_lock(mutex)
  #define rc_mutex_unlock(mutex)
 #else
-  #if defined(_WIN32)
+ #if defined(_WIN32)
    typedef struct rc_mutex_t {
    #if defined(WINVER) && WINVER >= 0x0600
      /* Windows Vista and later can use a slim reader/writer (SRW) lock */
@@ -97,6 +97,14 @@ RC_BEGIN_C_DECLS
      CRITICAL_SECTION critical_section;
    #endif
    } rc_mutex_t;
+ #elif defined(GEKKO)
+  #include <ogcsys.h>
+  typedef struct rc_mutex_t {
+    mutex_t handle;
+  } rc_mutex_t;
+ #elif defined(_3DS)
+  #include <3ds/synchronization.h>
+  typedef RecursiveLock rc_mutex_t;
  #else
   #include <pthread.h>
   typedef pthread_mutex_t rc_mutex_t;