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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202639 91177308-0d34-0410-b5e6-96231b3b80d8
[C++11] Switch from LLVM_STATIC_ASSERT to static_assert now that we
require host toolchains which support this.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202640 91177308-0d34-0410-b5e6-96231b3b80d8