[release-branch.go1.1] cmd/cgo: gccgo fixes

««« CL 11406047 / 4d9c3095de9d
cmd/cgo: gccgo fixes

Don't require a full-scale callback for calls to the special
prologue functions.

Always use a simple wrapper function for C functions, so that
we can handle static functions defined in the import "C"
comment.

Disable a test that relies on gc-specific function names.

Fixes #5905.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/11406047

»»»

Update #5928

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/11887043