Let ASan support depend on __has_feature(address_sanitizer) instead of defined(ADDRESS_SANITIZER)

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/213133002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20287 ce2b1a6d-e550-0410-aec6-3dcde31c8c00