mips64 elf64 reloc data structures

[Roland McGrath]

> I don't know how cleaner this, but here's what I'm working with now.

The formatting looks ok.  You have some "ytpe" comment typos.  The union
casts and struct/union constants are GCC extensions and if used in an
exported header should use __extension__.

> You mean, a private elf.h?  That would probably work just as well.

I suppose putting it in include/elf.h would be alright.