[Symtab][NFC] Added llvm_unreachable to supress compiler warning

Reviewers: JDevlieghere

Reviewed By: JDevlieghere

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D51587

llvm-svn: 341315

lldb/source/Symbol/Symtab.cpp

@@ -249,6 +249,7 @@ static bool lldb_skip_name(llvm::StringRef mangled,
   case Mangled::eManglingSchemeNone:
     return true;
   }
+  llvm_unreachable("unknown scheme!");
 }
 
 void Symtab::InitNameIndexes() {