Don't build on darwin.

Test: NA
Change-Id: I70279cf0c5e28749368441c1c312dfb8bc8994b3
diff --git a/Android.bp b/Android.bp
index 82c16a4..bb77bfb 100755
--- a/Android.bp
+++ b/Android.bp
@@ -11,6 +11,9 @@
         "math/*.c",
     ],
     target: {
+        darwin: {
+            enabled: false,
+        },
         linux_bionic: {
             enabled: true,
         },