[PATCH] D27565: [libcxx] Fix __compressed_pair so it doesn't copy the argument multiple times, and add constexpr.

[Eric Fiselier via Phabricator via cfe-commits]

EricWF added a reviewer: K-ballo.
EricWF added a subscriber: K-ballo.
EricWF added a comment.

@K-ballo if you have time would you do me the favor and looking this over.

In particular that I didn't accidentally change the layout of `__compressed_pair`. I don't think I did but I need a second set of eyes.
Here is a standalone header containing the old `__compressed_pair` implementation <https://gist.github.com/EricWF/554eea08b62148ff56ae84e7d32e1fbb>, because it's harder to read the diff.


https://reviews.llvm.org/D27565