- unpoison results from linux system call wrappers
- unpoison results from stat/fstat/lstat to pacify clang 14
(fixed in later versions)
- add MSAN build option
- turn on MSAN CI build
Previously they were just being run incorrectly, but nothing wrong with
the test itself. We were also interpreting an ASAN failure as TEST_SKIP,
so test failures would not actually be reported as CI failures.