[llvm] [NFC][LLVM] Use `StringRef` for Modifier in Inst/Asm Printers (PR #135403)

[Rahul Joshi via llvm-commits]

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@@ -31,7 +31,7 @@ class RISCVInstPrinter : public MCInstPrinter {
   void printRegName(raw_ostream &O, MCRegister Reg) override;
 
   void printOperand(const MCInst *MI, unsigned OpNo, const MCSubtargetInfo &STI,
-                    raw_ostream &O, const char *Modifier = nullptr);
+                    raw_ostream &O, StringRef Modifier = {});
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jurahul wrote:

SG, let me remove them where possible

https://github.com/llvm/llvm-project/pull/135403