Use a loop in generated code to allocate stack slots for function with many local...

Use a loop in generated code to allocate stack slots for function with many local variables.

If a function contains more than a certain number of locals (IA32: 9, X64: 6, ARM: 4)
a loop for initializing the locals with 'undefined' is more compact.
For less locals we unroll that loop by emitting a sequence of push instructions.

Review URL: http://codereview.chromium.org/515012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3521 ce2b1a6d-e550-0410-aec6-3dcde31c8c00