[libc++] Optimize ordered associative container insertion

[ldionne]

We seem to be very poorly in these operations, often 2x slower than other implementations.

[bassiounix]

What are the containers that you have in mind? Is there any information or examples to elaborate more on the issue?

[changkhothuychung]

@ldionne is there a container you have in mind with a suggested approach? I would like to give this a try,

[ldionne]

I'm closing this issue since it isn't precise enough to be actionable. @philnik777 has addressed some problems in eg #152691 but we still need to investigate map::insert(key_type const&). However we should do that with a dedicated issue.