[sanitizer] Fix test to tolerate chmod not working as intended

Attempts to fix a bot failure from
634da7a1 on an Android bot:
https://lab.llvm.org/buildbot#builders/77/builds/14339

It appears that the chmod is not making the directory unwritable as
expected on this system for some reason. Adopt an approach used in
compiler-rt/test/fuzzer/fuzzer-dirs.test for systems with
non-functioning chmod by including illegal characters in directory.