Open code the __fastfail intrinsic for rtabort! on windows

Open code the __fastfail intrinsic for rtabort! on windows

As described https://msdn.microsoft.com/en-us/library/dn774154.aspx

This is a Windows 8+ mechanism for terminating the process quickly,
which degrades to either an access violation or bugcheck in older versions.

I'm not sure this is better the the current mechanism of terminating
with an illegal instruction, but we recently converted unix to
terminate more correctly with SIGABORT, and this *seems* more correct
for windows.

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