When compiling JavaScriptCore for a 64-bit machine with MSVC, WebKitLibraries\win\include\stdint.h causes compile errors. I suggest lines 56-58 be changed from /* 7.18.1.4 Integer types capable of holding object pointers */ typedef int intptr_t; typedef unsigned uintptr_t; to this: /* 7.18.1.4 Integer types capable of holding object pointers */ typedef ptrdiff_t intptr_t; typedef size_t uintptr_t; This change works for 32 bit and 64 bit machines. This is not a part of the repository (it's installed with the script update-webkit --wincairo), so I cannot submit a patch.
wincairo should use http://trac.webkit.org/browser/trunk/Source/JavaScriptCore/os-win32/stdint.h instead. If that file does not work, a bug is ok. But for the wincairo files you should talk to Brent in the github repository at https://github.com/bfulgham/WinCairoRequirements, since they are not part of WebKit directly.
I uploaded a new WinCairoRequirements bundle that addresses this issue. This isn't a WebKit bug, but rather a build environment problem. Running "update-webkit --wincairo" should give you the new headers/binaries/link libraries. Note that I do not provide 64-bit builds in this bundle at present.