Silence these C4715 warnings from Visual C++ (NFC)

llvm\tools\lld\lib\readerwriter\macho\macholinkingcontext.cpp(647):
warning C4715: 'lld::MachOLinkingContext::exportSymbolNamed' :
not all control paths return a value

llvm\tools\lld\lib\readerwriter\macho\machonormalizedfilefromatoms.cpp(723):
warning C4715: '`anonymous namespace'::Util::getSymbolTableRegion' :
not all control paths return a value

While all enum values do appear in the switch, an uninitialized or corrupted
enum variable would not be caught without the default: case in the switch.

llvm-svn: 218197

lld/lib/ReaderWriter/MachO/MachOLinkingContext.cpp

@@ -643,6 +643,8 @@ bool MachOLinkingContext::exportSymbolNamed(StringRef sym) const {
     return _exportedSymbols.count(sym);
   case ExportMode::blackList:
     return !_exportedSymbols.count(sym);
+  default:
+    llvm_unreachable("_exportMode unknown enum value");
   }
 }
 

lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp

@@ -719,6 +719,9 @@ std::error_code Util::getSymbolTableRegion(const DefinedAtom* atom,
       return std::error_code();
     }
     break;
+  default:
+    llvm_unreachable("atom->scope() unknown enum value");
+    return std::error_code();
   }
 }