cmd/link/internal/ld: make runtime.buildVersion with experiments valid
Specifically if there are experiments but no nonstandard toolchain
suffix such as "-devel", the go version will not be valid according to
go/version.IsValid. To fix that, always put the X: part into the suffix,
resulting in, for example, go1.25.0-X:foo.
Fixes #75953
Change-Id: I6a6a696468f3ba9b82b6a410fb88831428e93b58
Reviewed-on: https://go-review.googlesource.com/c/go/+/719701 Reviewed-by: Michael Matloob <matloob@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>