We had no test for --hash-table in tools/llvm-readobj.
The one we had was in test/Object and checked that
it is possible to dump the hash table even when an object
doesn't have a section header table.
In this patch I created a test, moved and merged the existent one.
During moving I converted it to be YAML based to stop using the
precompiled binary.
Perhaps add a comment saying that we simulate no section header table by overriding the ELF header properties.