[MachineInstr] Use unsigned int for opcode (NFC)

[cdevadas]

Summary

The opcode field in most places uses unsigned type.
InstrInfoEmitter still uses signed int for the
custom opcodes like CFSetupOpcode.

llvm/utils/TableGen/InstrInfoEmitter.cpp

void InstrInfoEmitter::run(raw_ostream &OS) {
   // Create a TargetInstrInfo subclass to hide the MC layer initialization.
   OS << "#ifdef GET_INSTRINFO_HEADER\n";
   OS << "#undef GET_INSTRINFO_HEADER\n";
 
   std::string ClassName = TargetName + "GenInstrInfo";
   OS << "namespace llvm {\n";
   OS << "struct " << ClassName << " : public TargetInstrInfo {\n"
      << "  explicit " << ClassName
-     << "(int CFSetupOpcode = -1, int CFDestroyOpcode = -1, int CatchRetOpcode = -1, int ReturnOpcode = -1);\n"
+     << "(unsigned CFSetupOpcode = ~0u, unsigned CFDestroyOpcode = ~0u, "
+        "unsigned CatchRetOpcode = ~0u, unsigned ReturnOpcode = ~0u);\n"
      << "  ~" << ClassName << "() override = default;\n";
 
 
   OS << "\n};\n} // end namespace llvm\n";
 
   OS << "#endif // GET_INSTRINFO_HEADER\n\n";
 
   OS << "#ifdef GET_INSTRINFO_HELPER_DECLS\n";
void InstrInfoEmitter::run(raw_ostream &OS) {
   OS << "extern const char " << TargetName << "InstrNameData[];\n";
   if (HasDeprecationFeatures)
     OS << "extern const uint8_t " << TargetName
        << "InstrDeprecationFeatures[];\n";
   if (HasComplexDeprecationInfos)
     OS << "extern const MCInstrInfo::ComplexDeprecationPredicate " << TargetName
        << "InstrComplexDeprecationInfos[];\n";
   OS << ClassName << "::" << ClassName
-     << "(int CFSetupOpcode, int CFDestroyOpcode, int CatchRetOpcode, int "
-        "ReturnOpcode)\n"
+     << "(unsigned CFSetupOpcode, unsigned CFDestroyOpcode, unsigned "
+        "CatchRetOpcode, unsigned ReturnOpcode)\n"
      << "  : TargetInstrInfo(CFSetupOpcode, CFDestroyOpcode, CatchRetOpcode, "
         "ReturnOpcode) {\n"
      << "  InitMCInstrInfo(" << TargetName << "Insts, " << TargetName
      << "InstrNameIndices, " << TargetName << "InstrNameData, ";
   if (HasDeprecationFeatures)
     OS << TargetName << "InstrDeprecationFeatures, ";
   else
     OS << "nullptr, ";