Switch: Cleanup some includes.

Disable dlopen and tty checks too.

ext/native/base/stringutil.cpp

@@ -1,8 +1,13 @@
+#include "ppsspp_config.h"
 #ifdef _WIN32
 #include <windows.h>
 #undef min
 #undef max
 #endif
+#if PPSSPP_PLATFORM(SWITCH)
+#define _GNU_SOURCE
+#include <stdio.h>
+#endif
 #include <string.h>
 #include <stdarg.h>
 #include <errno.h>