common.gypi now contains global target defaults and is included by all .gyp files;
standalone.gypi contains definitions for stand-alone v8 builds.
This fixes d8 for the ARM simulator.

TEST=compiles and tests pass on all platforms

Review URL: http://codereview.chromium.org/7740020

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9019 ce2b1a6d-e550-0410-aec6-3dcde31c8c00