Disable mac-host build for libbrillo.

Bug: 72618679
Test: built on Mac locally.
Change-Id: I2f351f080770c3cfd67fb4c7d9c73ec0f53173be
diff --git a/Android.bp b/Android.bp
index a25205b..efb7b68 100644
--- a/Android.bp
+++ b/Android.bp
@@ -148,6 +148,9 @@
         android: {
             srcs: libbrillo_linux_sources,
         },
+        darwin: {
+            enabled: false
+        }
     },
 }