[llvm] [RISCV][NFC] Adopt DiagnosticString interface (PR #126290)

[Min-Yih Hsu via llvm-commits]

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@@ -150,12 +151,26 @@ def SPMem : MemOperand<SP>;
 
 def GPRCMem : MemOperand<GPRC>;
 
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mshockwave wrote:

I thought these (materialized) strings from TableGen code will eventually be put as normal C strings, so in the final compiler binaries similar string will still be deduplicated. Though these strings wouldn't be deduplicated in the *.inc files generated from TableGen I believe (though I think we can somehow solve this by changing how TableGen generates this part of the code)

https://github.com/llvm/llvm-project/pull/126290