[NFC] Make some ObjectFormatType switches covering

Summary:
This patch removes the `default` case from some switches on
`llvm::Triple::ObjectFormatType`, and cases for the missing enumerators
are then added.

For `UnknownObjectFormat`, the action (`llvm_unreachable`) for the
`default` case is kept.

For the other unhandled cases, `report_fatal_error` is used instead.

Reviewers: sfertile, jasonliu, daltenty

Reviewed By: sfertile

Subscribers: wuzish, aheejin, jsji, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D63767

llvm-svn: 365160

include/llvm/Support/TargetRegistry.h

@@ -470,7 +470,7 @@ public:
                                      bool DWARFMustBeAtTheEnd) const {
     MCStreamer *S;
     switch (T.getObjectFormat()) {
-    default:
+    case Triple::UnknownObjectFormat:
       llvm_unreachable("Unknown object format");
     case Triple::COFF:
       assert(T.isOSWindows() && "only Windows COFF is supported");
@@ -504,6 +504,8 @@ public:
         S = createWasmStreamer(Ctx, std::move(TAB), std::move(OW),
                                std::move(Emitter), RelaxAll);
       break;
+    case Triple::XCOFF:
+      report_fatal_error("XCOFF MCObjectStreamer not implemented yet.");
     }
     if (ObjectTargetStreamerCtorFn)
       ObjectTargetStreamerCtorFn(*S, STI);