add skip_module_validation label

Summary:
Add a label to modular libraries that are exporting non-modular deps. This will allow the upcoming tests to skip these targets for now.

#nocancel #retry_on_user_failure #notimeout #retry_on_timeout

Reviewed By: ebgraham

Differential Revision: D31320728

fbshipit-source-id: b1776d71168c282ff791030e530669a2341a9ac8

YogaKit/BUCK

@@ -42,6 +42,7 @@ yoga_apple_library(
         "$SDKROOT/System/Library/Frameworks/UIKit.framework",
     ],
     header_path_prefix = "",
+    labels = ["skip_module_validation"],
     link_whole = True,
     modular = True,
     module_name = "YogaKit",