This fixes a bug where 64 bit builds with /bigobj incorrectly determined
that the object files were not 64 bit. This manifested itself with
printf type functions showing up as undefined because the leading
underscore was being removed and should not be removed.
With 64-bit Windows builds, there is no need to remove the leading
underscore from all the symbols. This is because it does not have one
in the .obj file unless it is really in the name. This did not cause
any trouble until VS 2015 which has some system functions that have a
leading underscore that end up in the .def file.
Bill Hoffman