cmd/cgo: fix so that tests pass again when using gccgo
cmd/cgo: fix so that tests pass again when using gccgo

Use the symbol prefixes with the prologue functions when using
gccgo.

Use an & when referring to a function declared as a variable.

Fix the malloc prologue function.

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/13878043

wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,wesolows/golang