[Concurrency] An implementation of system epochs for continuous and suspending clocks

Author: phausler

stdlib/public/Concurrency/ContinuousClock.swift

@@ -139,6 +139,13 @@ extension ContinuousClock: Clock {
 #endif
 }
 
+@available(SwiftStdlib 5.7, *)
+extension ContinuousClock {
+  @available(SwiftStdlib 5.7, *)
+  @backDeployed(before: SwiftStdlib 9999)
+  public var systemEpoch: Instant { Instant(_value: .seconds(0)) }
+}
+
 @available(SwiftStdlib 5.7, *)
 @_unavailableInEmbedded
 extension ContinuousClock.Instant: InstantProtocol {

stdlib/public/Concurrency/SuspendingClock.swift

@@ -127,6 +127,13 @@ extension SuspendingClock: Clock {
 #endif
 }
 
+@available(SwiftStdlib 5.7, *)
+extension SuspendingClock {
+  @available(SwiftStdlib 5.7, *)
+  @backDeployed(before: SwiftStdlib 9999)
+  public var systemEpoch: Instant { Instant(_value: .seconds(0)) }
+}
+
 @available(SwiftStdlib 5.7, *)
 @_unavailableInEmbedded
 extension SuspendingClock.Instant: InstantProtocol {