This change introduces basic support for adding .dynamic entries to an ELF binary produced with yaml2obj.
* YAML traits for .dynamic section contents.
* `d_tag` can be populated by using the names of the tags.
* yaml2obj writes .dynamic entries.
* Some dynamic entries are validated for correctness.
* Some dynamic entries can be automatically inferred.
* Values can be numbers, strings (for things like DT_SONAME and DT_NEEDED, for example), or section names that are converted to addresses.
- SHT_DYNAMIC no longer supports the "Content" tag for sections that have raw content. This breaks `tools/llvm-objdump/private-headers-no-dynamic-segment.test`