Fix more build warnings

lib/Bitcode/NaCl/Reader/NaClBitCodes.cpp

 //===- NaClBitcodeHeader.cpp ----------------------------------------------===//
 //     PNaCl bitcode header reader.
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
@@ skipping 36 matching lines @@
   switch (NaClBitCodeAbbrevOp::Encoding(E)) {
   case Literal:
     return true;
   case Fixed:
   case VBR:
     return Val <= naclbitc::MaxAbbrevWidth;
   case Char6:
   case Array:
     return Val == 0;
   }
+  llvm_unreachable("unhandled abbreviation");
 }
 
 void NaClBitCodeAbbrevOp::Print(raw_ostream& Stream) const {
   if (Enc == Literal) {
     Stream << getValue();
     return;
   }
   Stream << getEncodingName(Enc);
   if (!hasValue())
     return;
@@ skipping 52 matching lines @@
   // Verify that an array op appears can only appear if it is the
   // second to last element.
   unsigned NumOperands = getNumOperandInfos();
   for (unsigned i = 0; i < NumOperands; ++i) {
     const NaClBitCodeAbbrevOp &Op = getOperandInfo(i);
     if (Op.isArrayOp() && i + 2 != NumOperands)
       return false;
   }
   return true;
 }