[committed] libstdc++: Implement LWG issues 3329, 3331, 3360, 3364, 3385

[Jonathan Wakely]

make common_iterator<I, S> require copyable<I> (LWG 3385)
Add default-initializers to views (LWG 3364)
Simplify std::three_way_comparable_with (LWG 3360)
Simplify std::totally_ordered (LWG 3331)
Simplify std::totally_ordered_with (LWG 3329)

Tested powerpc64le-linux, committed to master.


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