`-C link-arg=-Wl,-z,pack-relative-relocs`

This enables a new relocation format, which is more compact. Supported since glibc 2.36, GNU Binutils 2.38 and LLVM 15 according to https://rfc.archlinux.page/0023-pack-relative-relocs/.

See <https://maskray.me/blog/2021-10-31-relative-relocations-and-relr> for details.

