cmd/compile: note escape of parts of closured-capture vars
Missed a case for closure calls (OCALLFUNC && indirect) in
esc.go:esccall.
Cleanup to runtime code for windows to more thoroughly hide
a technical escape. Also made code pickier about failing
to late non-optional kernel32.dll.
Revised for 1.6.2
Fixes #14409.
Change-Id: Ie75486a2c8626c4583224e02e4872c2875f7bca5
Reviewed-on: https://go-review.googlesource.com/22050
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Andrew Gerrand <adg@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>