Fix obscure problem with using the system linker (#8935)

See Note [RTLD_LOCAL] for a summary of the problem and solution, and
Raise exceptions when blocked in bad FDs (fixes Trac #4934)

Before the patch any call to 'select()' with 'bad_fd' led to:
- unblocking of all threads
- hiding exception for 'threadWaitRead bad_fd'

The patch fixes both cases in this way:
after 'select()' failure we iterate over each blocked descriptor
and poll individually to see it's actual status, which is:
- READY (move to run queue)
- BLOCKED (leave in blocked queue)
- INVALID (send an IOErrror exception)

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Remove unused --run-cps/--run-cpsz options
Don't use showPass in the backend (#8973)