This renames the existing V8_ALIGNAS() to V8_ALIGNED(), and introduces
V8_ALIGNAS(type, alignment) which aligns according to the type and falls
back to aligning according to alignment.

Also use __attribute__((aligned(n))) instead of __attribute__((__aligned__(n))).

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/22999052

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16318 ce2b1a6d-e550-0410-aec6-3dcde31c8c00