Attempted buildfix for Apple

Author: LibretroAdmin

ui/drivers/cocoa/cocoa_common.m

@@ -17,6 +17,8 @@
 #import <AvailabilityMacros.h>
 #include <sys/stat.h>
 
+#include <string/stdstring.h>
+
 #include "cocoa_common.h"
 #include "apple_platform.h"
 #include "../ui_cocoa.h"