Implement assume_aligned using the standard API

This implements `Eigen::internal::assume_aligned` to match the API for C++20 standard as best as possible using either `std::assume_aligned` or `__builtin_assume_aligned` if available. If neither is available, the function is a no-op.

The override macro `EIGEN_ASSUME_ALIGNED` was changed to a `EIGEN_DONT_ASSUME_ALIGNED`, which now forces the function to be a no-op.

See merge request libeigen/eigen!2052


(cherry picked from commit 8716f109e465d4122e61be9087b17a48bf58ca45)

f8191848 Fix pcmp_* for HVX to to comply with the new definition of true = Scalar(1).
7cc169d9 Revert "Fix pcmp_* for HVX to to comply with the new definition of true = Scalar(1)."
06999845 Merge branch eigen:master into master
b5fde61f Merge branch eigen:master into master
10d10d60 Merge branch eigen:master into master
9398d6ad Merge branch eigen:master into master
7804d5a4 Merge branch eigen:master into master
0068623c Merge branch eigen:master into master
b0ffc9cf Merge branch eigen:master into master
f3791c80 Merge branch eigen:master into master
74275f0c Merge branch eigen:master into master
b095614e Merge branch eigen:master into master
1312a696 Merge branch eigen:master into master
e6dd44d2 Merge branch eigen:master into master
8ac67769 Implement assume_aligned using the standard API if available.
97b299fa Format.
b31798be Fix typos.
04b3d312 Unformat.

Co-authored-by: Rasmus Munk Larsen <rmlarsen@google.com>
3 files changed