Fixing the Mac SDK build

recovery_host_test is now excluded from darwin targets as its
dependency libimgdiff is.

Change-Id: I6aa085125109ed2218572df97f35289b71c354ab
diff --git a/tests/Android.bp b/tests/Android.bp
index d305e25..a880b76 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -215,4 +215,11 @@
     ],
 
     data: ["testdata/*"],
+
+    target: {
+        darwin: {
+            // libimgdiff is not available on the Mac.
+            enabled: false,
+        },
+    },
 }