runtime: record full frame size for arm _sfloat2
runtime: record full frame size for arm _sfloat2

With preemption, _sfloat2 can show up in stack traces.
Write the function prototype in a way that accurately
shows the frame size and the fact that it might contain
pointers.

R=golang-dev, dvyukov
CC=golang-dev
https://codereview.appspot.com/11523043

d0f/go-zh,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,webfd/go-zh,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,rdp/rogerpack2005-golang,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,bryanxu/go-zh,webfd/go-zh,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,bryanxu/go-zh,bryanxu/go-zh,d0f/go-zh,rdp/rogerpack2005-golang,mhennings/marcohennings-go,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,rdp/rogerpack2005-golang,d0f/go-zh,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,mhennings/marcohennings-go,rdp/rogerpack2005-golang,d0f/go-zh,bryanxu/go-zh,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,mhennings/marcohennings-go,mhennings/marcohennings-go,bryanxu/go-zh,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof