FileToHdr-related fix for building 64 bit windows core FDO projects.

[edzimmerman]

For now, the current FDO windows 64 bit porting effort assumes that most developers will be building the x64 version of FDO on x86 win32 machines using the x86_amd64 cross compiler. This means that when building the x64 platform configuration, the FDO.sln must build the win32 version of the FileToHdr preprocessing utility called by the custom build steps in the Common.vcproj and Fdo.vcproj. Furthermore, the x64 configurations of Common.vcproj and Fdo.vcproj need to refer to the win32 version of the FileToHdr utility in the relevant custom build steps.