cmd/cgo: strip top-level const qualifier from argument frame struct
Otherwise we can't assign to it.
Fixes #75751
Change-Id: Iba680db672297bca1a1d1a33912b80863da66a08
Reviewed-on: https://go-review.googlesource.com/c/go/+/717342 Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org> Reviewed-by: Mark Freeman <markfreeman@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>