[release-branch.go1.12] cmd/cgo: fix inappropriate array copy

Ensure that during rewriting of expressions that take the address of
an array, that we properly recognize *ast.IndexExpr as an operation
to create a pointer variable and thus assign the proper addressOf
and deference operators as "&" and "*" respectively.

This fixes a regression from CL 142884.

This is a backport of CLs 183458 and 183778 to the 1.12 release branch.
It is not a cherry pick because the code in misc/cgo/test has changed.

Updates #32579
Fixes #32756

Change-Id: I0daa75ec62cccbe82ab658cb2947f51423e0c235
Reviewed-on: https://go-review.googlesource.com/c/go/+/183627


Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>