Return the number of read bytes in MemoryObject::readBytes.

Returning more information will allow BitstreamReader to be simplified a bit
and changed to read 64 bits at a time.

llvm-svn: 221794

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -3430,7 +3430,7 @@ std::error_code BitcodeReader::InitLazyStream() {
   Stream.init(&*StreamFile);
 
   unsigned char buf[16];
-  if (Bytes->readBytes(0, 16, buf) == -1)
+  if (Bytes->readBytes(buf, 16, 0) != 16)
     return Error(BitcodeError::InvalidBitcodeSignature);
 
   if (!isBitcode(buf, buf + 16))