This patch implements support of ELF input format in the obj2yaml tool.
Please note that now the ELF header e_flags field in the MIPS related test cases handled incorrectly. The obj2yaml prints too many flags. I will fix that in the next patches.
Now the llvm::yaml::Output class prints quotes for strings which are valid numbers. The string 0000023C... is not a valid octal number. Do you suggest to implement a general solution and always print quotes for all string which starts from a digit even if the rest of the string is not a valid number? This greatly simplify the isNumber function from the YAMLTraits.h, but I am still note sure that we need so general modification.
I wouldn't be opposed to being more conservative when quoting in general. I think that the extra quotes would probably be a net win for the human reader, which has a much harder time knowing if it is an octal number.
That can be a separate patch though. The current patch LGTM.