cmd/compile: fix re-export closure

For hidden closure built during stenciling to implement a function
instantiation, the function may come from other package, not local
package, which causes the ICE for code that re-export the hidden closure
after inlining.

To fix it, use the closure package for export writer when writing out
the closure itself.

Fixes #51423

Change-Id: I23b067ba14e2d602a0fc3b2e99bd9317afbe53ff
Reviewed-on: https://go-review.googlesource.com/c/go/+/391574


Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>