This should fix firm-testsuite/fehler242.c

This puts the special logic for cfops into the common code instead of
repeating it in all schedulers.

I don't see a reason why this would be bad, and I have such a case now
so I removed the assert.

We now add missing keeps exactly before register allocation where we
actually need them (so that unused outputs which still need registers
assigned are not missed by the register allocation).

Previously we had an AR commandline that replaced old object files with newer
ones in the archive. This however fails when we remove files from the
project, because the previous objects in the archive were not removed
(and often caused missing symbol errors when linking later).
So now I remove the archive each time before creating it, to make up for
the speed loss use the "thin archive" option. This is not a good idea
for a release/installed version of libfirm, but for that we still use
the automake build anyway.

This sort of typeless programming is bad style and deprecated.

This removes functions from the public API which are pointless outside
localopt rules, and also avoids another struct in the public API.

This could result in blocks getting asked for their block, which
happened in firm-testsuite/opt/combo10.c