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/rust/Android.bp b/libs/binder/rust/Android.bp
index dc8270e..fd5f2f5 100644
--- a/libs/binder/rust/Android.bp
+++ b/libs/binder/rust/Android.bp
@@ -10,6 +10,11 @@
         "libbinder_ndk_sys",
     ],
     host_supported: true,
+    target: {
+        darwin: {
+            enabled: false,
+        }
+    }
 }
 
 rust_library {
@@ -23,6 +28,11 @@
         "libbinder_ndk",
     ],
     host_supported: true,
+    target: {
+        darwin: {
+            enabled: false,
+        }
+    }
 }
 
 rust_bindgen {
@@ -64,6 +74,9 @@
                 "-D__ANDROID_API__=10000",
             ],
         },
+        darwin: {
+            enabled: false,
+        },
     },
 }