[llvm] [SPIR-V] Route ISel errors through diagnoseUnsupported (PR #196899)

[Arseniy Obolenskiy via llvm-commits]

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@@ -1418,8 +1418,8 @@ bool SPIRVInstructionSelector::selectExtInst(Register ResVReg,
     std::string DiagMsg;
     raw_string_ostream OS(DiagMsg);
     I.print(OS, true, false, false, false);
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aobolensk wrote:

Agree, done

https://github.com/llvm/llvm-project/pull/196899