[release-branch.go1.24] os: don't follow symlinks on Windows when O_CREATE|O_EXCL

[release-branch.go1.24] os: don't follow symlinks on Windows when O_CREATE|O_EXCL

(This cherry-pick includes both CL 672396 and CL 676655.)

Match standard Unix behavior: Symlinks are not followed when
O_CREATE|O_EXCL is passed to open.

Thanks to Junyoung Park and Dong-uk Kim of KAIST Hacking Lab
for discovering this issue.

For #73702
Fixed #73720
Fixes CVE-2025-0913

Change-Id: Ieb46a6780c5e9a6090b09cd34290f04a8e3b0ca5
Reviewed-on: https://go-review.googlesource.com/c/go/+/672396
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/677215
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Bypass: Michael Knyszek <mknyszek@google.com>