Default to host VM for Art/Dalvik when not specified

Change-Id: I51324ee3352eaff882bbdb190525617ae8adb9d7
diff --git a/src/test/java/com/android/tools/r8/ToolHelper.java b/src/test/java/com/android/tools/r8/ToolHelper.java
index f73f198..4f8b2e3 100644
--- a/src/test/java/com/android/tools/r8/ToolHelper.java
+++ b/src/test/java/com/android/tools/r8/ToolHelper.java
@@ -713,6 +713,12 @@
       return DexVm.ART_DEFAULT;
     } else {
       DexVm artVersionEnum = DexVm.fromShortName(artVersion);
+      if (artVersionEnum == null
+          && !artVersion.endsWith(Kind.HOST.toString())
+          && !artVersion.endsWith(Kind.TARGET.toString())) {
+        // Default to host Art/Dalvik when not specified.
+        artVersionEnum = DexVm.fromShortName(artVersion + '_' + Kind.HOST.toString());
+      }
       if (artVersionEnum == null) {
         throw new RuntimeException("Unsupported Art version " + artVersion);
       } else {