Add file_setup.sh to streamline first-time setup for each file

tools/split_asm.py

@@ -40,7 +40,10 @@ if __name__ == '__main__':
             current_file.close()
 
     if args.c_base != None:
+        os.makedirs(os.path.dirname(args.c_base), exist_ok=True)
         with open(args.c_base, 'w') as f:
+            f.write('#include <ultra64.h>\n#include <global.h>\n\n')
+
             for name in file_names:
                 f.write('GLOBAL_ASM("{}")\n\n'.format(name))