Added missing SDL_sysfilesystem.h includes

src/filesystem/emscripten/SDL_sysfilesystem.c

@@ -24,6 +24,9 @@
 
 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 /* System dependent filesystem routines                                */
+
+#include "../SDL_sysfilesystem.h"
+
 #include <errno.h>
 #include <sys/stat.h>