MIPS32: peek*/poke*, and String.charAt intrinsics.

- byte libcore.io.Memory.peekByte(long address)
- short libcore.io.Memory.peekShort(long address)
- int libcore.io.Memory.peekInt(long address)
- long libcore.io.Memory.peekLong(long address)
- void libcore.io.Memory.pokeByte(long address, byte value)
- void libcore.io.Memory.pokeShort(long address, short value)
- void libcore.io.Memory.pokeInt(long address, int value)
- void libcore.io.Memory.pokeLong(long address, long value)
- char java.lang.String.charAt(int index)

Change-Id: I5ff30b61d87313d00f0fd3f0ee09f1c454f9c9fa
diff --git a/compiler/optimizing/code_generator_mips64.h b/compiler/optimizing/code_generator_mips64.h
index c836f83..12a5fc6 100644
--- a/compiler/optimizing/code_generator_mips64.h
+++ b/compiler/optimizing/code_generator_mips64.h
@@ -351,7 +351,7 @@
 
   void MoveFromReturnRegister(Location trg ATTRIBUTE_UNUSED,
                               Primitive::Type type ATTRIBUTE_UNUSED) OVERRIDE {
-    UNIMPLEMENTED(FATAL);
+    UNIMPLEMENTED(FATAL) << "Not implemented on MIPS64";
   }
 
  private: