[test] Fix Container::insert(value_type const&) tests

Patch from Joe Loser.

Several unit tests meaning to test the behavior of lvalue insertion incorrectly
pass rvalues. Fixes bug PR # 27394

Reviewed as https://reviews.llvm.org/D44411


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@329541 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed