Simplify raw mode lexing by treating an unterminate /**/ comment the

Simplify raw mode lexing by treating an unterminate /**/ comment the
same we we do an unterminated string or character literal.  This makes
it so we can guarantee that the lexer never calls into the
preprocessor (which would be suicide for a raw lexer).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@57395 91177308-0d34-0410-b5e6-96231b3b80d8