Joe Loser 2513b79030
[libc++] Implement LWG3549: view_interface need not inherit from view_base
Implement LWG3549 by making `view_interface` not inherit from `view_base`. Types
are still views if they have a public and unambiguous derivation from
`view_interface`, so adjust the `enable_view` machinery as such to account for
that.

Differential Revision: https://reviews.llvm.org/D117714
2022-01-22 22:52:46 -05:00
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