Clang is a bit more strict wrt format-nonliterals:
http://clang.llvm.org/docs/LanguageExtensions.html#format-string-checking
Adding these extra printf attributes also makes gcc able to find more
problems. E.g. this patch uncovers a format issue in udev-builtin-path_id.c
Some parts looked intetional about breaking the format-nonliteral check.
I added some supression for warnings there.
b8a2b0f76 'use initalization instead of explicit zeroing'
introduced a bug where only the first sizeof(uint_t*) bytes
would be zeroed out, instead of the whole array.