sys-boot/elilo: fix build failure on ia64 against gnu-efi-3.0.6

sys-boot/elilo: fix build failure on ia64 against gnu-efi-3.0.6

Disambiguate setpjmp()/longjmp()/jmp_buf implementation across
elilo copy and gnu-efi-3.0.6.

To avoid behaviour change I'm keeping elilo's implementation for now
as the jmp_buf passing ABI is slightly different across the two.

```
  setjmp.h:25:14: error: conflicting types for 'jmp_buf'
   typedef long jmp_buf[_JBLEN] __attribute__ ((aligned (16)));
                ^~~~~~~
  In file included from /usr/include/efi/efisetjmp.h:5:0,
                   from /usr/include/efi/efi.h:60,
                   from gzip.c:29:
  /usr/include/efi/ia64/efisetjmp_arch.h:45:23: note: previous
    declaration of 'jmp_buf' was here
   } ALIGN(JMPBUF_ALIGN) jmp_buf;
                         ^~~~~~~
```

Reported-by: Stanton Arch
Package-Manager: Portage-2.3.28, Repoman-2.3.9