ninja/win: Put common msvs_system_include_dirs into %INCLUDE% 

Paths in INCLUDE are considered system headers by clang-cl and it will suppress 
warnings from system headers. 

BUG=chromium:395405
Review URL: https://codereview.chromium.org/406523005/


git-svn-id: http://gyp.googlecode.com/svn/trunk@1953 78cadc50-ecff-11dd-a971-7dbc132099af
3 files changed