[C++11] Replace llvm::tie with std::tie.

[C++11] Replace llvm::tie with std::tie.

The old implementation is no longer needed in C++11.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202644 91177308-0d34-0410-b5e6-96231b3b80d8