Use pointers to iterate over symbols.

While here, don't report a dummy symbol for relocations that don't have symbols.
We used to says such relocations were for the first defined symbol, but now we
return end_symbols(). The llvm-readobj output change agrees with otool.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180214 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/llvm-readobj/MachODumper.cpp b/tools/llvm-readobj/MachODumper.cpp
index 10e53d9..31dc5ce 100644
--- a/tools/llvm-readobj/MachODumper.cpp
+++ b/tools/llvm-readobj/MachODumper.cpp
@@ -345,7 +345,9 @@
   if (error(RelI->getOffset(Offset))) return;
   if (error(RelI->getTypeName(RelocName))) return;
   if (error(RelI->getSymbol(Symbol))) return;
-  if (error(Symbol.getName(SymbolName))) return;
+  if (symbol_iterator(Symbol) != Obj->end_symbols() &&
+      error(Symbol.getName(SymbolName)))
+    return;
 
   DataRefImpl DR = RelI->getRawDataRefImpl();
   macho::RelocationEntry RE = Obj->getRelocation(DR);