Scan-build and scan-view installation

Hi, all!

I tried to implement support for installation of scan-build and
scan-view (see https://llvm.org/bugs/show_bug.cgi?id=23761).

It work on Linux for me, but help is needed with other platforms.
Obviously Windows should install .bat files instead of scripts without
extensions. Probably scan-view should be renamed to scan-view.py for
Windows support.

I'm also not sure that GNUInstallDirs is best way to install files and
used for other parts of LLVM.

Eugene.

Hello,