[SYCL][Driver] Enable full clang driver unit tests on Windows

[AGindinson]

Several sycl-offload*.c LITs under clang/test/Driver are marked with 'XFAIL: windows-msvc'. The failures are seemingly related to some path regexp issue. New tests addition also faces this limitation, e.g. #884.

This XFAIL need to be analyzed and fixed as soon as possible to provide better.

[mdtoguchi]

Most of the problems deal with using FileCheck -DOBJ=%t.obj type checks and trying to match with [[OBJ]]. This doesn't look to work too well on Windows perhaps due to the additional escapes used for the directory separators and dots.

Is there any way to work around this?