See bug 33383. WebCore forwarding headers have a special header guard style.
Thanks for the report!
It looks like the rule here is if dir includes /([^/]*)/ForwardingHeaders/, then the header guard should be $1_FWD_NormalHeaderGuard
It seems JavaScriptCore/ForwardingHeaders/**/*.h, WebKit/mac/ForwardingHeaders/**/*.h, and WebKitTools/DumpRenderTree/ForwardingHeaders/**/*.h don't contain #ifndef guards. Maybe we can just silence build/header_guard for ForwardingHeaders? I'm not sure if it's worth to implement the check of $1_FWD_ style header guard only for WebCore.
Created attachment 49360 [details] Patch v1
> Patch v1 This patch just disables header guard checks as I proposed in Comment 3.
Comment on attachment 49360 [details] Patch v1 Clearing flags on attachment: 49360 Committed r55184: <http://trac.webkit.org/changeset/55184>
All reviewed patches have been landed. Closing bug.