Return ErrorOr from SymbolRef::getName.

This function can really fail since the string table offset can be out of
bounds.

Using ErrorOr makes sure the error is checked.

Hopefully a lot of the boilerplate code in tools/* can go away once we have
a diagnostic manager in Object.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241297 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Object/MachO.h

@@ -199,8 +199,7 @@ public:
   void moveSymbolNext(DataRefImpl &Symb) const override;
 
   uint64_t getNValue(DataRefImpl Sym) const;
-  std::error_code getSymbolName(DataRefImpl Symb,
-                                StringRef &Res) const override;
+  ErrorOr<StringRef> getSymbolName(DataRefImpl Symb) const override;
 
   // MachO specific.
   std::error_code getIndirectName(DataRefImpl Symb, StringRef &Res) const;