Update to use XTENSOR_DEFAULT_ALIGNMENT when using XSIMD

[spectre-ns]

Checklist

• [ x] The title and commit message(s) are descriptive.
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Description

Updated to allow overriding of alignment when using XSIMD. If the user doesn't provide an overriding value then the default XSIMD value is used. This fixed linker issues when different default vectorization settings are used between libraries within the same project. The intel C++ compiler requests 16 alignment for AVX while MSVC defines it to 32 so it's nice to be able to pin the alignment at the higher of the two.

[JohanMabille]

Thanks!