Clang installation is not auto-detected for Windows

Clang officially ships windows builds at http://llvm.org/releases/download.html

They even have nightly builds http://llvm.org/builds/

Clang on Windows works by using Visual C++ 2013/2015 headers and CRT.

Qt Creator could check for the presence of `HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\LLVM\LLVM`.

and then high jack existing Visual C++ kits by changing the following
environment variables:

$ set PATH=C:\Program Files (x86)\LLVM\msbuild-bin\;%PATH%
$ set INCLUDE=C:\Program Files (x86)\LLVM\lib\clang\3.7.0\include\;%INCLUDE%

Then everything should work as would normally do for Visual C++.

Currently the LLVM 64 bit installer suffers from the following bug:
https://llvm.org/bugs/show_bug.cgi?id=26212

Clang on Windows is too important not to support.

With minimum effort Qt Creator 3.7.0 could have some nice PR! – Clang supported on Windows!