[Driver] Driver changes to support CUDA compilation on Windows.

Summary:
For the most part this is straightforward: Just add a CudaInstallation
object to the MSVC and MinGW toolchains.

CudaToolChain has to override computeMSVCVersion so that
Clang::constructJob passes the right version flag to cc1.  We have to
modify IsWindowsMSVC and friends in Clang::constructJob to be true when
compiling CUDA device code on Windows for the same reason.

Depends on: D28319

Reviewers: tra

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D28320

llvm-svn: 291131