Introduce the 'link_dependency' attribute that removes the targets having this
attribute from the 'none' targets' dependencies.

The intention behind this change is to let the users have static_library or
shared_library targets on which _every_ other executable/shared_library target
must depend, without introducing excessive dependencies on the former ones from
the 'none' metatargets (such excessive dependencies may trigger generator bugs
like https://code.google.com/p/gyp/issues/detail?id=409).

Patch by Alexander Potapenko <glider@chromium.org>

Review URL: https://codereview.chromium.org/177043010/


git-svn-id: http://gyp.googlecode.com/svn/trunk@1860 78cadc50-ecff-11dd-a971-7dbc132099af