Disable libbinder darwin builds

libbinder makes heavy use of linux headers, so it won't build on a mac.
This gives us cleaner errors when a mac target depends on it. Instead of
seeing libbinder build breakages, we will see the missing dependency
error.

Exempt-From-Owner-Approval: fixing build breakage

Test: none
Bug: 172023026
Change-Id: I4eadf2c9c09599b5d1bcafdb7d8559946c854e49
diff --git a/libs/binder/ndk/Android.bp b/libs/binder/ndk/Android.bp
index e4d86ae..cecc759 100644
--- a/libs/binder/ndk/Android.bp
+++ b/libs/binder/ndk/Android.bp
@@ -26,6 +26,9 @@
                 "-D__ANDROID_API__=10000",
             ],
         },
+        darwin: {
+            enabled: false,
+        },
     },
 }
 
@@ -84,6 +87,9 @@
         linux: {
             version_script: "libbinder_ndk.map.txt",
         },
+        darwin: {
+            enabled: false,
+        },
     },
     stubs: {
         symbol_file: "libbinder_ndk.map.txt",