Lexer: split test into separate files

Unfortunately, XFAIL applies to the entire file.  Split the test into two
different units, enabling the proper application of XFAIL on the test which is
expected to fail on Windows.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203633 91177308-0d34-0410-b5e6-96231b3b80d8