functions and the ones defined on the AST nodes take a code generator,
rather than a macro assembler and (sometimes) scope.

Uniformly use the __ macro for masm_/masm in the codegen*.cc files.
Review URL: http://codereview.chromium.org/5663

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@408 ce2b1a6d-e550-0410-aec6-3dcde31c8c00