schedcore: Make buildable on !linux

Fixes: #5983

sched-core only makes sense on Linux hosts. Let's add stub/error for
other platforms.

Signed-off-by: Eric Ernst <eric_ernst@apple.com>
Signed-off-by: Danny Canter <danny@dcantah.dev>

src/runtime/pkg/utils/schedcore_linux.go

@@ -0,0 +1,20 @@
+// Copyright (c) 2023 Apple Inc.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package utils
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+// Create a new sched core domain
+func Create(t PidType) error {
+	return unix.Prctl(unix.PR_SCHED_CORE, unix.PR_SCHED_CORE_CREATE, 0, uintptr(t), 0)
+}
+
+// ShareFrom shares the sched core domain from the provided pid
+func ShareFrom(pid uint64, t PidType) error {
+	return unix.Prctl(unix.PR_SCHED_CORE, unix.PR_SCHED_CORE_SHARE_FROM, uintptr(pid), uintptr(t), 0)
+}