The build settings involved in deciding whether the shims are linked at build time or inserted at runtime are defined in terms of the SDK version rather than the target version.
Created attachment 267266 [details]
Base shim-related build settings on target OS X version
Fixed in <http://trac.webkit.org/r194018>.
Build fix in <http://trac.webkit.org/r194019>.
Follow-up fix in <http://trac.webkit.org/r194023>.