implement the null function for the Mips32 subzero compiler

src/IceAssemblerMIPS32.h

 //===- subzero/src/assembler_mips.h - Assembler for MIPS --------*- C++ -*-===//
 //
 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // Modified by the Subzero authors.
 //
 //===----------------------------------------------------------------------===//
 //
@@ skipping 29 matching lines @@
     (void)use_far_branches;
   }
   ~AssemblerMIPS32() override = default;
 
   void alignFunction() override {
     llvm::report_fatal_error("Not yet implemented.");
   }
 
   SizeT getBundleAlignLog2Bytes() const override { return 4; }
 
-  const char *getNonExecPadDirective() const override { return ".TBD"; }
+  const char *getNonExecPadDirective() const override { return ".p2alignl"; }
 
   llvm::ArrayRef<uint8_t> getNonExecBundlePadding() const override {
-    llvm::report_fatal_error("Not yet implemented.");
+    // TBD (Reed Kotler ) . Find out what this should be.

[jvoung (off chromium), 2015/06/12 19:39:12]

nit: Usually we try to format the "TODO"s consistently as TODO(username), so
that it's easier to grep for.

E.g., you have TODO(reed kotler) in some other places.

+    static const uint8_t Padding[] = {0xE7, 0xFE, 0xDE, 0xF0};
+    return llvm::ArrayRef<uint8_t>(Padding, 4);
   }
 
   void padWithNop(intptr_t Padding) override {
     (void)Padding;
     llvm::report_fatal_error("Not yet implemented.");
   }
 
   void bindCfgNodeLabel(SizeT NodeNumber) override {
     (void)NodeNumber;
     llvm::report_fatal_error("Not yet implemented.");
   }
 
   bool fixupIsPCRel(FixupKind Kind) const override {
     (void)Kind;
     llvm::report_fatal_error("Not yet implemented.");
   }
 };
 
 } // end of namespace MIPS32
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ASSEMBLER_MIPS32_H