Fix memory leak in set and map.

When assigning an initializer list into set/map, libc++ would
leak memory if the initializer list contained equivalent keys
because we failed to check if the insertion was successful.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@365840 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed