Object file support for s390x (#2872)

Add support for s390x binary format object files.  In particular,
add support for s390x ELF relocation types (currently only
S390xPCRel32Dbl).

crates/debug/src/lib.rs

@@ -120,6 +120,7 @@ fn ensure_supported_elf_format(bytes: &mut Vec<u8>) -> Result<Endianness, Error>
 
     match header.e_machine.get(e) {
         EM_X86_64 => (),
+        EM_S390 => (),
         machine => {
             bail!("Unsupported ELF target machine: {:x}", machine);
         }