Disable building libapplypatch on mac

The sdk_mac on build server fails with the error:
bootable/recovery/applypatch/freecache.cpp:23:10: fatal error: 'sys/statfs.h' file not found

So we will disable libapplypatch on mac.

Test: the library still builds on linux; and check the other host targets in the same cl.
Change-Id: Ie4a30708726e51c810f7ad7f1085d38154076cca
diff --git a/applypatch/Android.bp b/applypatch/Android.bp
index d3efa15..cb0b367 100644
--- a/applypatch/Android.bp
+++ b/applypatch/Android.bp
@@ -57,6 +57,12 @@
         "libotautil",
         "libz",
     ],
+
+    target: {
+        darwin: {
+            enabled: false,
+        },
+    },
 }
 
 cc_library_static {