Merging r315994:

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r315994 | ericwf | 2017-10-17 06:03:17 -0700 (Tue, 17 Oct 2017) | 18 lines

[libc++] Fix PR34898 - vector iterator constructors and assign method perform push_back instead of emplace_back.

Summary:
The constructors `vector(Iter, Iter, Alloc = Alloc{})` and `assign(Iter, Iter)` don't correctly perform EmplaceConstruction from the result of dereferencing the iterator. This results in them performing an additional and unneeded copy.

This patch addresses the issue by correctly using `emplace_back` in C++11 and newer.

There are also some bugs in our `insert` implementation, but those will be handled separately.

@mclow.lists We should probably merge this into 5.1, agreed?

Reviewers: mclow.lists, dlj, EricWF

Reviewed By: mclow.lists, EricWF

Subscribers: cfe-commits, mclow.lists

Differential Revision: https://reviews.llvm.org/D38757
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git-svn-id: https://llvm.org/svn/llvm-project/libcxx/branches/release_50@318837 91177308-0d34-0410-b5e6-96231b3b80d8
12 files changed