[clang] Guard against self-assignment; NFC (PR #145743)

[Aaron Ballman via cfe-commits]

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@@ -6410,9 +6410,11 @@ class SpirvOperand {
   ~SpirvOperand() {}
 
   SpirvOperand &operator=(const SpirvOperand &Other) {
-    this->Kind = Other.Kind;
-    this->ResultType = Other.ResultType;
-    this->Value = Other.Value;
+    if (this != &Other) {
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AaronBallman wrote:

That would require C++20, wouldn't it?

https://github.com/llvm/llvm-project/pull/145743