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
This CL adds support for extension in GYP.

This CL adds the extension target type and adds the link flags to
compile .appex extensions.

BUG=gyp:435
R=justincohen@chromium.org, mark@chromium.org, pkl@chromium.org, sdefresne@chromium.org

Review URL: https://codereview.chromium.org/376603002

git-svn-id: http://gyp.googlecode.com/svn/trunk@1954 78cadc50-ecff-11dd-a971-7dbc132099af
ninja: Add support for 'ninja_use_console' in actions/rules

Setting this to 1 will make ninja use 'pool = console' for the action/rule.

BUG=
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/412283002

git-svn-id: http://gyp.googlecode.com/svn/trunk@1955 78cadc50-ecff-11dd-a971-7dbc132099af