I'm using the post call generator for the macro assembler
InvokeBuiltin call to be consistent with the ia32 version. It only
generates one call, but using the post call generator it should be
easier to catch if we change that at some point.

Review URL: http://codereview.chromium.org/6119004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6247 ce2b1a6d-e550-0410-aec6-3dcde31c8c00