Some ELF binaries contain alternative or old ELF machine types, which
should match with their canonical forms. Map those before encoding the
ABI.

We ignore some mappings for things that should certainly never appear
in current systems. Of note are EM_PPC_OLD (17) that conflicts with
EM_VPP550 (17), and EM_PJ_OLD (99) that conflicts with EM_SNP1K (99).

Warned-by: rebootstrap