[lld] [lld][BP] Avoid ordering ICF'ed sections (PR #126327)

[Fangrui Song via llvm-commits]

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@@ -117,6 +117,8 @@ DenseMap<const InputSection *, int> lld::macho::runBalancedPartitioning(
         auto *isec = subsec.isec;
         if (!isec || isec->data.empty())
           continue;
+        if (isa<ConcatInputSection>(isec) && !isec->isLive(0))
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MaskRay wrote:

`off` is for mergeable string and constant literals. It is unneeded for ` // ConcatInputSections are entirely live or dead, so the offset is irrelevant.`

While I haven't verified, I suspect that we only need to pass `ConcatInputSection` to BP if Mach-O works like ELF.

https://github.com/llvm/llvm-project/pull/126327