[llvm-branch-commits] [llvm-objdump] -r: support CREL (PR #97382)

[Fangrui Song via llvm-branch-commits]

https://github.com/MaskRay created https://github.com/llvm/llvm-project/pull/97382

The decoder code is similar to that for llvm-readelf -r (#91280).

Because the section representation of LLVMObject (`SectionRef`) is
64-bit, insufficient to hold all decoder states, `section_rel_begin` is
modified to decode CREL eagerly and hold the decoded relocations inside
ELFObjectFile<ELFT>.

The test is adapted from llvm/test/tools/llvm-readobj/ELF/crel.test.