[lit] Don't disable the lit progress bar by default with MSVC

Only disable the progress bar when we're generating VS project files,
like we do for XCode. This makes lit use the simple, non-curses progress
bar that looks like this with:

Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..
Testing Time: 5.87s

llvm-svn: 244674