debug/elf: add machine and OSABI constants

Provide a complete list of EM_* and ELFOSABI_* constants.

Compiled from the tables at
http://www.sco.com/developers/gabi/latest/ch4.eheader.html
and llvm/BinaryFormat/ELF.h from LLVM.

Change-Id: Ice1e1476076fafdb8bb8af848caec6d80a82c452
Reviewed-on: https://go-review.googlesource.com/112115
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>