Fix mac build

Move darwin disabling to art_test_defaults to disable mac build for
libarttest.

Test: mmma -j art on mac
Change-Id: I972245ddbacea274087d9231e4788bd9f2d6fe6b
diff --git a/test/Android.bp b/test/Android.bp
index 1256960..ff408f4 100644
--- a/test/Android.bp
+++ b/test/Android.bp
@@ -36,6 +36,9 @@
         android_x86_64: {
             relative_install_path: "art/x86_64",
         },
+        darwin: {
+            enabled: false,
+        },
     },
 }
 
@@ -94,9 +97,6 @@
                 "-Wno-missing-noreturn",
             ],
         },
-        darwin: {
-            enabled: false,
-        },
         android: {
             ldflags: [
                 // Allow jni_compiler_test to find Java_MyClassNatives_bar