Update Eigen to commit:3368ac6c6934af3d7c16b05727084b4e08d07497

CHANGELOG
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3368ac6c6 - Don't set platform-specific vectorization macros for generic backend.
fecfa7f27 - Fixes to make generic backend build with AVX512
ec93a6d09 - Add a generic Eigen backend based on clang vector extensions

PiperOrigin-RevId: 829252717
Change-Id: I563971d8eb82645cb07f78e983e18fca732b7f44
18 files changed