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-objdump/COFFDump.cpp b/tools/llvm-objdump/COFFDump.cpp
index 2ada683..7b55007 100644
--- a/tools/llvm-objdump/COFFDump.cpp
+++ b/tools/llvm-objdump/COFFDump.cpp
@@ -178,7 +178,7 @@
     uint64_t Ofs;
     if (error_code ec = I->getOffset(Ofs)) return ec;
     if (Ofs == Offset) {
-      if (error_code ec = I->getSymbol(Sym)) return ec;
+      Sym = *I->getSymbol();
       break;
     }
   }