locale: Implemented SDL_GetPreferredLocales().

This was something I proposed a long time ago, Sylvain Becker did
additional work on it, then back to me.

Fixes Bugzilla #2131.

src/core/android/SDL_android.h

@@ -104,6 +104,9 @@ void Android_JNI_InitTouch(void);
 JNIEnv *Android_JNI_GetEnv(void);
 int Android_JNI_SetupThread(void);
 
+/* Locale */
+int Android_JNI_GetLocale(char *buf, size_t buflen);
+
 /* Generic messages */
 int Android_JNI_SendMessage(int command, int param);