[libcxx] adds spaceship for vector

[cjdb]

Summary

[libcxx] adds spaceship for vector

• adds C++20 operator== for vector
• adds operator<=> for vector

Note: This is currently WIP due to being unable to find tests for vector's comparison operations.

[miscco]

libcxx/include/compare

679

This is usually spelled as ifndef _LIBCPP_HAS_NO_SPACESHIP_OPERATOR

686

I have to look it up but what about string orderings here?

libcxx/include/vector

3339

Same here #ifndef _LIBCPP_HAS_NO_SPACESHIP_OPERATOR

[cjdb]

libcxx/include/compare

686

See http://eel.is/c++draft/expos.only.func#2.

[miscco]

libcxx/include/compare

686

Thanks a lot, I thought I read it in some blog, but that is way better