Add some missing checks for C++1y digit separators that don't in fact separate
digits. Turns out we have completely separate lexing codepaths for floating
point numbers depending on whether or not they start with a zero. Who knew...
=)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206932 91177308-0d34-0410-b5e6-96231b3b80d8