[asan] Disable strict init checking on AIX (#178012)
The `__cxa_atexit` interceptor is disabled for `SANITIZER_AIX` because
Clang on AIX neither uses `__cxa_atexit` nor links against a library
with such. This interceptor calls `StopInitOrderChecking()`, which is
needed to prevent false positives for the `initialization-order-fiasco`
error observed in the asan test `init-order-atexit.cpp` that uses the
`strict_init_order` flag. For now, we'll disable the `strict_init_order`
flag, but we'll look to support it in the future by implementing an
`exit` interceptor or some other alternative. With the flag disabled, we
won't update `init-order-atexit.cpp` to ensure it continues to pass and
the false positive doesn't show up.
