Simplify the handling of iterators in ObjectFile.

None of the object file formats reported error on iterator increment. In
retrospect, that is not too surprising: no object format stores symbols or
sections in a linked list or other structure that requires chasing pointers.
As a consequence, all error checking can be done on begin() and end().

This reduces the text segment of bin/llvm-readobj in my machine from 521233 to
518526 bytes.

llvm-svn: 200442
diff --git a/llvm/tools/llvm-ar/llvm-ar.cpp b/llvm/tools/llvm-ar/llvm-ar.cpp
index 8917cd3..bb5c0da 100644
--- a/llvm/tools/llvm-ar/llvm-ar.cpp
+++ b/llvm/tools/llvm-ar/llvm-ar.cpp
@@ -716,10 +716,9 @@
       print32BE(Out, 0);
     }
 
-    error_code Err;
     for (object::symbol_iterator I = Obj->begin_symbols(),
                                  E = Obj->end_symbols();
-         I != E; I.increment(Err), failIfError(Err)) {
+         I != E; ++I) {
       uint32_t Symflags;
       failIfError(I->getFlags(Symflags));
       if (Symflags & object::SymbolRef::SF_FormatSpecific)