Disable libbootloader_message for darwin

libfstab is not built for darwin, don't build libbootloader_message
either.

Bug: 131709594
Test: m PRODUCT-sdk-sdk sdk_repo
Change-Id: I6e3b04f1c3e97d5aa6ac0452bf13e714f8dae437
diff --git a/bootloader_message/Android.bp b/bootloader_message/Android.bp
index 4ea7c86..e76305f 100644
--- a/bootloader_message/Android.bp
+++ b/bootloader_message/Android.bp
@@ -41,6 +41,9 @@
             static_libs: [
                 "libfstab",
             ],
-        }
+        },
+        darwin: {
+            enabled: false,
+        },
     }
 }