Cleanup v8.gyp. This also drops a bunch of unused targets (the shell, d8,

etc).

There are now two gyp variables to control whether we build snapshots and which
target we are building for.  This allows you to easily cross-compile for arm and
disable snapshots.

Patch by Joel Stanley.

Original review: http://codereview.chromium.org/149243

Review URL: http://codereview.chromium.org/155218


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2392 ce2b1a6d-e550-0410-aec6-3dcde31c8c00