chore: import upstream snapshot with attribution

Sources/ContainerizationOS/Syscall.swift

@@ -0,0 +1,39 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 Apple Inc. and the Containerization project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+#if canImport(Musl)
+import Musl
+#elseif canImport(Glibc)
+import Glibc
+#elseif canImport(Darwin)
+import Darwin
+#else
+#error("retryingSyscall not supported on this platform.")
+#endif
+
+/// Helper type to deal with running system calls.
+public struct Syscall {
+    /// Retry a syscall on EINTR.
+    public static func retrying<T: FixedWidthInteger>(_ closure: () -> T) -> T {
+        while true {
+            let res = closure()
+            if res == -1 && errno == EINTR {
+                continue
+            }
+            return res
+        }
+    }
+}