Parse cgo's "export" comments
Parse cgo's "export" comments

Functions can be marked with an "//export" comment and cgo will use that
to allow C world to call these Go functions. This can mean that a Go
function is never used by Go and only by C.

Mark these functions as roots.

Closes gh-32

dominikh/go-tools,dominikh/go-tools,dominikh/go-tools,dominikh/go-tools