[DirectX] Fix two "not all control paths return a value" warnings

[bogner]

Summary

These switch statements are fully covered. Add an llvm_unreachable so
that compilers that don't recognize that don't warn.

[beanz]

LGTM

llvm/lib/Target/DirectX/DXILResource.cpp

case ComponentType::SNormF64:
     return "snorm_f64";
   case ComponentType::UNormF64:
     return "unorm_f64";
   case ComponentType::PackedS8x32:
     return "p32i8";
   case ComponentType::PackedU8x32:
     return "p32u8";
   }
+  llvm_unreachable("All ComponentType enums are handled in switch");
 }
 
 void ResourceBase::printComponentType(Kinds Kind, ComponentType CompType,
                                       unsigned Alignment, raw_ostream &OS) {
   switch (Kind) {
   default:
     // TODO: add vector size.
     OS << right_justify(getComponentTypeName(CompType), Alignment);
case Kinds::TBuffer:
     return "tbuffer";
   case Kinds::RTAccelerationStructure:
     return "ras";
   case Kinds::FeedbackTexture2D:
     return "fbtex2d";
   case Kinds::FeedbackTexture2DArray:
     return "fbtex2darray";
   }
+  llvm_unreachable("All Kinds enums are handled in switch");
 }
 
 void ResourceBase::printKind(Kinds Kind, unsigned Alignment, raw_ostream &OS,
                              bool SRV, bool HasCounter, uint32_t SampleCount) {
   switch (Kind) {
   default:
     OS << right_justify(getKindName(Kind), Alignment);
     break;