Dwarf: implement .eh_frame

[jacobly0]

No description provided.

[kubkon]

Perhaps it would make sense to land elf-incr branch first (#21212) in its current state since it cleans up a lot of things in the ELF linker, and then rebase this branch on top? Next, initSyntheticSections really should not be used in initMetadata - happy to clean that one up if you want. Finally, not a blocker but as it currently stands, .eh_frame generated with ZigObject will not have its CIEs deduped across all input object files - not a biggie, but something to remember about. I would also like to have it tested with the linker - emit .eh_frame section as part of .o file and then link it back into an executable.

[jacobly0]

Finally, not a blocker but as it currently stands, .eh_frame generated with ZigObject will not have its CIEs deduped across all input object files - not a biggie, but something to remember about. I would also like to have it tested with the linker - emit .eh_frame section as part of .o file and then link it back into an executable.

A CIE is like 24 bytes, so it's definitely not worth deduping the two extra CIE per module in incremental mode (the only use case I'm working towards right now), especially given all the padding that already exists. The key feature that would be useful is the ability to generate a .eh_frame_hdr in non-incremental mode, which I believe would come for free when CIE deduping is integrated.

[kubkon]

Looks great!