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/lib/Object/Object.cpp b/lib/Object/Object.cpp
index 3e2c78e..6941708 100644
--- a/lib/Object/Object.cpp
+++ b/lib/Object/Object.cpp
@@ -219,10 +219,7 @@
 }
 
 LLVMSymbolIteratorRef LLVMGetRelocationSymbol(LLVMRelocationIteratorRef RI) {
-  SymbolRef ret;
-  if (error_code ec = (*unwrap(RI))->getSymbol(ret))
-    report_fatal_error(ec.message());
-
+  symbol_iterator ret = (*unwrap(RI))->getSymbol();
   return wrap(new symbol_iterator(ret));
 }