Handle relocations that don't point to symbols.

In ELF (as in MachO), not all relocations point to symbols. Represent this
properly by using a symbol_iterator instead of a SymbolRef. Update llvm-readobj
ELF's dumper to handle relocatios without symbols.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183284 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/llvm-readobj/COFFDumper.cpp b/tools/llvm-readobj/COFFDumper.cpp
index 94aafa7..3cbb9b3 100644
--- a/tools/llvm-readobj/COFFDumper.cpp
+++ b/tools/llvm-readobj/COFFDumper.cpp
@@ -201,8 +201,7 @@
       return EC;
 
     if (Ofs == Offset) {
-      if (error_code EC = RelI->getSymbol(Sym))
-        return EC;
+      Sym = *RelI->getSymbol();
       return readobj_error::success;
     }
   }
@@ -670,14 +669,13 @@
   uint64_t Offset;
   uint64_t RelocType;
   SmallString<32> RelocName;
-  SymbolRef Symbol;
   StringRef SymbolName;
   StringRef Contents;
   if (error(RelI->getOffset(Offset))) return;
   if (error(RelI->getType(RelocType))) return;
   if (error(RelI->getTypeName(RelocName))) return;
-  if (error(RelI->getSymbol(Symbol))) return;
-  if (error(Symbol.getName(SymbolName))) return;
+  symbol_iterator Symbol = RelI->getSymbol();
+  if (error(Symbol->getName(SymbolName))) return;
   if (error(SecI->getContents(Contents))) return;
 
   if (opts::ExpandRelocs) {