[llvm] [perf] Replace copy-assign by move-assign in llvm/lib/MC/* (PR #178176)

[Simon Pilgrim via llvm-commits]

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@@ -212,7 +212,7 @@ struct FieldInfo {
 StructFieldInfo::StructFieldInfo(std::vector<StructInitializer> V,
                                  StructInfo S) {
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RKSimon wrote:

A lot of the other structs in this file passes by rvalue - why doesn't StructFieldInfo?

https://github.com/llvm/llvm-project/pull/178176