Sam Weinig says that the definition of WTF_USE_AVFOUNDATION on Windows should be moved back to JavaScriptCore/wtf/Platform.h from WebCore/config.h. We'll have to move the generated file WebCore/WebCoreHeaderDetection.h as well.
<rdar://problem/10056527>
We did this on the Mac in bug 67316. <https://bugs.webkit.org/show_bug.cgi?id=67316>
This was done ages ago!