Fix dex2oat cross-compilation.

The instruction set features was not correctly set when it was not
given in the command line.

Change-Id: I649cc077e7bbc830d281ae59af43e59fd0541c1b
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index 223be4c..326fa72 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -837,7 +837,7 @@
   InstructionSet instruction_set = kRuntimeISA;
   std::string error_msg;
   std::unique_ptr<const InstructionSetFeatures> instruction_set_features(
-      InstructionSetFeatures::FromFeatureString(instruction_set, "default", &error_msg));
+      InstructionSetFeatures::FromFeatureString(kNone, "default", &error_msg));
   CHECK(instruction_set_features.get() != nullptr) << error_msg;
 
   // Profile file to use
@@ -1152,6 +1152,13 @@
     oat_unstripped += oat_filename;
   }
 
+  // If no instruction set feature was given, use the default one for the target
+  // instruction set.
+  if (instruction_set_features->GetInstructionSet() == kNone) {
+    instruction_set_features.reset(
+      InstructionSetFeatures::FromFeatureString(instruction_set, "default", &error_msg));
+  }
+
   if (compiler_filter_string == nullptr) {
     if (instruction_set == kMips64) {
       // TODO: fix compiler for Mips64.