[lld] [lld][ELF] Introduce an option to keep data section prefix. (PR #148985)

[Fangrui Song via llvm-commits]

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+# REQUIRES: x86
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MaskRay wrote:

>From a patch organization perspective, it would be clearer to first introduce the option in a patch and then add RELRO semantics in a follow-up patch (#148920). While it's unusual that 148920 was merged first, the changes remain on the right track... I would rename this to keep-data-section-prefix.s, not introducing a separate test file.

https://github.com/llvm/llvm-project/pull/148985