Fixes a detected error: incompatible pointer to integer conversion
passing 'uv_os_fd_t' (aka 'void *') to parameter of type 'SOCKET' (aka
'unsigned long long').
Use upstream llvm to work-around broken VS2022 clang unable to link.
- 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.
