Always load the JavaScript builtins code entry from the JavaScript

Always load the JavaScript builtins code entry from the JavaScript
function instead of baking in the address of the first one that we see
in code.

This removes the need for fixups processing and makes the stubs safe
when there is no natives cache and therefore multiple versions of the
builtin functions.

Review URL: http://codereview.chromium.org/594009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3832 ce2b1a6d-e550-0410-aec6-3dcde31c8c00