[Base] Use function-local static for global_mutex

File-scope static initialization order is undefined across translation
units. Code that acquires the global critical region during early startup
could run before the mutex constructor, operating on uninitialized state.
A function-local static is constructed on first use, guaranteeing the
mutex is initialized before any caller can access it.

src/xenia/base/mutex.cc

@@ -65,9 +65,9 @@ bool xe_fast_mutex::try_lock() {
   return TryEnterCriticalSection(fast_crit(this));
 }
 #endif
-// chrispy: moved this out of body of function to eliminate the initialization
+global_mutex_type& global_critical_region::mutex() {
-// guards
+  static global_mutex_type global_mutex;
-static global_mutex_type global_mutex;
+  return global_mutex;
-global_mutex_type& global_critical_region::mutex() { return global_mutex; }
+}
 
 }  // namespace xe