Fix Windows build after r198766.

* Source/cmake/WebKitMacros.cmake:
Use the filename from the cpp so that WebCorePrefix.cpp and WebCoreDerivedSourcesPrefix.cpp 
generate unique .pch files, even though they both include WebCorePrefix.h



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@198772 268f45cc-cd09-0410-ab3c-d52691b4dbfc
2 files changed