Use the return of readBytes to find out if we are at the end of the stream.

This allows the removal of isObjectEnd and opens the way for reading 64 bits
at a time.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221804 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/StreamingMemoryObject.h

@@ -38,7 +38,6 @@ public:
     return nullptr;
   }
   bool isValidAddress(uint64_t address) const override;
-  bool isObjectEnd(uint64_t address) const override;
 
   /// Drop s bytes from the front of the stream, pushing the positions of the
   /// remaining bytes down by s. This is used to skip past the bitcode header,