illumos gate

To facilitate features in the link editor that are unsuitable for relocatable objects in general, but acceptable for kernel modules (the first being linker-sets, future examples possibly including -zcombreloc, for eg), the link-editor should know that kernel modules are a distinct kind of object.

Do this by implementing an Oracle-style -ztype that takes =kmod, which clues in the link-editor, and sets a dynamic tag usable by other software
Make ld(1) refuse to accept a kmod as link-editor input (we currently, unfortunately, do that with genunix), teach file(1) to spot the flag for kernel modules.