Enable equality comparisons on GPU.

Antonio Sánchezrequested to merge
cantonios/eigen:cuda_equal into master

Since std::equal_to::operator() is not a device function, it fails on GPU. On my device, I seem to get a silent crash in the kernel (no reported error, but the kernel does not complete).

Replacing this with a portable version enables comparisons on device.

Addresses #2292 (closed) - would need to be cherry-picked. The 3.3 branch also requires adding EIGEN_DEVICE_FUNC in BooleanRedux.h to get fully working.

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