runtime, crypto/x509: fix vet complaints for all windows

Working toward making the tree vet-safe instead of having
so many exceptions in cmd/vet/all/whitelist.

This CL makes "go vet -unsafeptr=false runtime" happy for windows/*,
while keeping "GO_BUILDER_NAME=misc-vetall go tool dist test" happy too.

For #31916.

Change-Id: If37ab2b3f6fca4696b8a6afb2ef11ba6c4fb42e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/176106


Reviewed-by: Austin Clements <austin@google.com>