fixes for warnings/errors with clang on MacOS

It's been a while, but once again I compiled the entire AnalysisBase release on my laptop and fixed all warnings and errors. Hopefully this is all uncontroversial and can just be merged as is. I purposely kept the changes minimal, as I'm not the package responsible for (most of) these packages. I purposely made a separate commit for each package to make sweeping easier, so please don't check the box to merge the commits.

Also a short ping to @akraszna: It would be great if we could add the -Wno-deprecated flag to building dictionaries. For one, dictionaries may very well automatically include deprecated methods, for another the way we build dictionaries already produces a deprecation warning on MacOS by itself.

clang: warning: treating 'c-header' input as 'c++-header' when in C++ mode, this behavior is deprecated [-Wdeprecated]