clangcl bot for Windows

[GoogleCodeExporter]

Windows can be built with clangcl.
Add a bot to test this.
Getting started should cover how to build, but here is a quick summary.

::Do this once per repo
set GYP_DEFINES=clang=1 target_arch=ia32
set LLVM_REPO_URL=svn://svn.chromium.org/llvm-project
call python tools\clang\scripts\update.py

::Build with GYP_DEFINES=clang=1
call python gyp_libyuv -fninja libyuv_test.gyp
ninja -C out\Debug
ninja -C out\Release

clang\scripts\update.py is quite slow, so it can be by passed if you already 
have clang
build clang once and put it in a folder.  Then add make_clang_dir to 
GYP_DEFINES:
set GYP_DEFINES=clang=1 make_clang_dir=../../myllvm/build 

Original issue reported on code.google.com by fbarch...@chromium.org on 24 Mar 2015 at 5:48