So I am still waiting for my access to the compile farm being activated!
Yesterday I filed a support ticket with respect to these failures. I am not the only one with these problem as this site shows (once you set the category to SF.net Compile farm).
Now I wonder whether this is a good thing or not: On the one hand a problem observed by many folks is quite likely to be fixed. Otherwise one ticket dates back to November 23 and doesn't appear to be resolved yet.