[RISCV] Implement multiVersionSortPriority

[BeMg]

Summary

Default implementation will return 0 for all case. It will cause the random function mangling name.

[jrtc27]

I don't think you can just use any arbitrary function?

clang/lib/Basic/Targets/RISCV.h

public:
   bool useFP16ConversionIntrinsics() const override {
     return false;
   }
 
   bool isValidCPUName(StringRef Name) const override;
   void fillValidCPUList(SmallVectorImpl<StringRef> &Values) const override;
   bool isValidTuneCPUName(StringRef Name) const override;
   void fillValidTuneCPUList(SmallVectorImpl<StringRef> &Values) const override;
+  unsigned multiVersionSortPriority(StringRef Name) const override;
 };
 class LLVM_LIBRARY_VISIBILITY RISCV32TargetInfo : public RISCVTargetInfo {
 public:
   RISCV32TargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
       : RISCVTargetInfo(Triple, Opts) {
     IntPtrType = SignedInt;
     PtrDiffType = SignedInt;
     SizeType = UnsignedInt;

clang/lib/Basic/Targets/RISCV.cpp

bool RISCVTargetInfo::isValidTuneCPUName(StringRef Name) const {
   return llvm::RISCV::parseTuneCPU(Name, Is64Bit);
 }
 
 void RISCVTargetInfo::fillValidTuneCPUList(
     SmallVectorImpl<StringRef> &Values) const {
   bool Is64Bit = getTriple().isArch64Bit();
   llvm::RISCV::fillValidTuneCPUArchList(Values, Is64Bit);
 }
+unsigned RISCVTargetInfo::multiVersionSortPriority(StringRef Name) const {
+  return llvm::RISCVISAInfo::getExtensionSerial(Name);
+}