[lld] [ELF] --package-metadata: support %[0-9a-fA-F][0-9a-fA-F] (PR #126396)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Thanks! The feature is quite isolated. Creating a cherry-pick in case it does get more uses on Ubuntu.

/cherry-pick 0a470a926481d370251731cb2dd897531756335f

https://github.com/llvm/llvm-project/pull/126396