Various fixes

@pino Pretty please, whenever you can, check this changes. The first one is what I would do to fix the autopkgtests running with different clang versions than the one used at build time, the rest are backports of patches I've found in the satble 1.6 branch of clazy.

My worries lie mostly in the first change (same clang/llvm version), you might have a better idea. For the rest most of them are debatible, but I think they will not hurt.

I am going to test build this on amd64 and try to cross build it on i386.