Fix host oat_test on portable.

Change-Id: I8d72b89dc8a7dc9243ce77551a8a01a10c5ec9ce
diff --git a/runtime/oat_test.cc b/runtime/oat_test.cc
index 9fb2638..5d0dca9 100644
--- a/runtime/oat_test.cc
+++ b/runtime/oat_test.cc
@@ -74,7 +74,8 @@
 #else
   CompilerBackend compiler_backend = kQuick;
 #endif
-  compiler_driver_.reset(new CompilerDriver(compiler_backend, kThumb2, false, NULL, 2, true));
+  InstructionSet insn_set = kIsTargetBuild ? kThumb2 : kX86;
+  compiler_driver_.reset(new CompilerDriver(compiler_backend, insn_set, false, NULL, 2, true));
   jobject class_loader = NULL;
   if (compile) {
     base::TimingLogger timings("OatTest::WriteRead", false, false);