Driver: default to `-fno-use-cxatexit` on Windows

This primarily impacts the Windows MSVC and Windows itanium
environments.  Windows MSVC does not use `__cxa_atexit` and Itanium
follows suit.  Simplify the logic for the default value calculation and
blanket the Windows environments to default to off for use of
`__cxa_atexit`.

llvm-svn: 312941