Add -std=c++1z flag for C++17 features.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@211030 91177308-0d34-0410-b5e6-96231b3b80d8
[C++1z] Implement N4051: 'typename' is permitted instead of 'class' when declaring a template template parameter.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@211031 91177308-0d34-0410-b5e6-96231b3b80d8