utils/llvm-lit: Generate "llvm-lit.py" rather than "llvm-lit" on Win32 hosts...

utils/llvm-lit: Generate "llvm-lit.py" rather than "llvm-lit" on Win32 hosts to let llvm-lit.py --use-processes work.

llvm-lit needs suffix.py for multiprocess to find a main module.

llvm-svn: 196328