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The short answer is that you’d expect lib to be built (or rather, installed) if there’s a library to install, and include if there are headers to install. Usually the two go together (at least for C and C++ libraries).

In binutils’ case, the library and associated headers are libbfd, which is a library used to manipulate object files in a variety of formats. It is installed by default for same-host compilation, but not for cross-compilation, which is why you’re seeing different behaviour in your scenarios. You can see the conditional default in bfd/acinclude.m4 in the source code.