[lld] [ELF] Prevent .eh_frame_hdr size oscillation in address assignment (PR #216248)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay requested changes to this pull request.

This is correct as a follow-up to #179089, but please don't merged until I approve to ensure the test is in a good shape. 

(#pranavk "Approving but may want to wait for others" doesn't actually hold the patch:  the author can address comments and land without lld/ELF maintainers seeing it. Please leave it as Comment, or name who to wait for. This has happened several times with colleague approvals where neither party is a frequent contributor to the area, so I've become strict about it.)

https://github.com/llvm/llvm-project/pull/216248