IRGen: change switch to be covered

Rather than adding a default case, add the missing case and rely on covered
switches providing indications of future additions.  NFC.

Author: compnerd

lib/IRGen/IRGenModule.cpp

@@ -877,6 +877,8 @@ void IRGenModule::emitAutolinkInfo() {
                         AutolinkEntries.end());
 
   switch (TargetInfo.OutputObjectFormat) {
+  case llvm::Triple::UnknownObjectFormat:
+    llvm_unreachable("unknown object format");
   case llvm::Triple::MachO: {
     llvm::LLVMContext &ctx = Module.getContext();
 
@@ -921,9 +923,6 @@ void IRGenModule::emitAutolinkInfo() {
     addUsedGlobal(var);
     break;
   }
-  default:
-    llvm_unreachable("Don't know how to emit autolink entries for "
-                     "the selected object format.");
   }
 
   if (!IRGen.Opts.ForceLoadSymbolName.empty()) {