Add dynamic_table iterators back to ELF.h.

In tree they are only used by llvm-readobj, but it is also used by
https://github.com/mono/CppSharp.

While at it, add some missing error checking.

llvm-svn: 244320

llvm/lib/Object/Error.cpp

@@ -47,6 +47,8 @@ std::string _object_error_category::message(int EV) const {
     return "Invalid section index";
   case object_error::bitcode_section_not_found:
     return "Bitcode section not found in object file";
+  case object_error::elf_invalid_dynamic_table_size:
+    return "Invalid dynamic table size";
   case object_error::macho_small_load_command:
     return "Mach-O load command with size < 8 bytes";
   case object_error::macho_load_segment_too_many_sections: