Per updates to D3781, allow underscore under ' in a pp-number, and allow ' in a #line directive.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191443 91177308-0d34-0410-b5e6-96231b3b80d8
Add macro test from N3781.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191444 91177308-0d34-0410-b5e6-96231b3b80d8