Default to usejit:true.

Manually verified places that could be affected (go/lem, buildbots, CTS).
Also adjust two tests expecting JIT.

bug: 64164063
Test: m and tests
Change-Id: I6dc441f0f58203546480a0f7220ad4d9cd593fd3
diff --git a/runtime/parsed_options.cc b/runtime/parsed_options.cc
index a44e5a4..0d98d90 100644
--- a/runtime/parsed_options.cc
+++ b/runtime/parsed_options.cc
@@ -518,9 +518,12 @@
     LOG(INFO) << "setting boot class path to " << *args.Get(M::BootClassPath);
   }
 
-  if (args.GetOrDefault(M::UseJitCompilation) && args.GetOrDefault(M::Interpret)) {
-    Usage("-Xusejit:true and -Xint cannot be specified together");
-    Exit(0);
+  if (args.GetOrDefault(M::Interpret)) {
+    if (args.Exists(M::UseJitCompilation) && *args.Get(M::UseJitCompilation)) {
+      Usage("-Xusejit:true and -Xint cannot be specified together\n");
+      Exit(0);
+    }
+    args.Set(M::UseJitCompilation, false);
   }
 
   // Set a default boot class path if we didn't get an explicit one via command line.