runtime: export cgoCheck functions
The functions cgoCheckPointer and cgoCheckResult are called by code
generated by cgo. That means that we need to export them using
go:linkname, as otherwise they are local symbols. The cgo code
currently uses weak references to only call the symbols if they are
defined, which is why it has been working--the cgo code has not been
doing any checks.
Reviewed-on: https://go-review.googlesource.com/80295
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@255347 138bc75d-0d04-0410-961f-82ee72b054a4