Use conditional store to replace the receiver with undefined for
strict mode functions and builtins instead of branching code. This
has similar performance characteristics but saves one branch
instruction per strict mode function.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/48473002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17412 ce2b1a6d-e550-0410-aec6-3dcde31c8c00