[llvm] Add support to YAML for program headers with content. (PR #192364)

[James Henderson via llvm-commits]

jh7370 wrote:

See https://github.com/llvm/llvm-project/blob/main/llvm/test/tools/yaml2obj/ELF/custom-fill.yaml for the yaml2obj test that covers these fill sections. As you'll see from the test, you can specify them with FirstSec/LastSec in the same manner as other sections.

With regards to obj2yaml, reading every gap between file chunks (sections/file header/section header table etc) is probably impractical, but we could read the program headers at least, to have bidirectional support for core files.

@MaskRay, as someone who has had plenty of experience using yaml2obj, what do you think?

https://github.com/llvm/llvm-project/pull/192364