section and allow this type to be overridden.
The ELF specification says it should always be uint32_t (Elf_Word), but
alpha decided to be different (not sure why). Define Elf_Symindx to be
uint64_t on alpha.
Alpha no longer uses non-standard definitions of Elf64_Sword and
Elf64_Word. Remove the ability to override these types.
Fixes ld.elf_so after Herculean effort from me and martin.