This tweaks the CMake rules for building an installation package on Windows:
- Sets license file (otherwise nsis shows an ugly default)
- Adds LLVM logo
- Shows "do you want to add this to the system path" dialog.
Differential Revision: http://llvm-reviews.chandlerc.com/D1414
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188509 91177308-0d34-0410-b5e6-96231b3b80d8
