Don't wait indefinitely to gather stack traces

barrier_block_until_poked() may signal failure with a value other
than -1. In particular, if the controlling thread decides time
has run out, it closes the pipe which may cause poll() to signal
POLLNVAL in revents for waiting threads, leading them to see
barrier_block_until_poked() return -2.

Also general cleanup; use OMR_ARE_ANY_BITS_SET, OMR_ARE_NO_BITS_SET.

Signed-off-by: Keith W. Campbell <[email protected]>