build with 64-bit time_t on 32-bit platforms (swiftlang#82595)

It is good practice to build with 64-bit `time_t`/timeval on 32-bit
platforms to avoid the Y2038 issue. This is the default when building on
Yocto for armv7, for example. Unfortunately `suseconds_t` is not an
alias to a type of the correct width (unlike time_t).

Question: on release/6.1, tv_usec is assumed to be `Int32`, but on main
it is `Int`, but appears to be the same commit hash?

#### git blame main stdlib/public/Platform/Platform.swift

```
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 350) @available(SwiftStdlib 5.7, *)
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 351) extension timeval {
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 352)   @available(SwiftStdlib 5.7, *)
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 353)   public init(_ duration: Duration) {
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 354)     let comps = duration.components
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 355)   // Linux platforms define timeval as Int/Int
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 356)   self.init(tv_sec: Int(comps.seconds),
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 357)               tv_usec: Int(comps.attoseconds / 1_000_000_000_000))
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 358)   }
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 359) }
```

#### git blame release/6.1 stdlib/public/Platform/Platform.swift

```
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 455) @available(SwiftStdlib 5.7, *)
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 456) extension timeval {
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 457)   @available(SwiftStdlib 5.7, *)
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 458)   public init(_ duration: Duration) {
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 459)     let comps = duration.components
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 460) #if os(Linux)
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 461)   // Linux platforms define timeval as Int/Int
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 462)   self.init(tv_sec: Int(comps.seconds),
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 463)               tv_usec: Int(comps.attoseconds / 1_000_000_000_000))
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 464) #else
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 465)     // Darwin platforms define timeval as Int/Int32
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 466)     self.init(tv_sec: Int(comps.seconds),
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 467)               tv_usec: Int32(comps.attoseconds / 1_000_000_000_000))
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 468) #endif
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 469)   }
e675b31 (Philippe Hausler    2022-02-17 09:32:46 -0800 470) }
```

Author: lhoward

stdlib/public/Platform/Platform.swift

@@ -334,7 +334,7 @@ extension timespec {
   @available(SwiftStdlib 5.7, *)
   public init(_ duration: Duration) {
     let comps = duration.components
-    self.init(tv_sec: Int(comps.seconds),
+    self.init(tv_sec: time_t(comps.seconds),
               tv_nsec: Int(comps.attoseconds / 1_000_000_000))
   }
 }
@@ -352,9 +352,19 @@ extension timeval {
   @available(SwiftStdlib 5.7, *)
   public init(_ duration: Duration) {
     let comps = duration.components
-  // Linux platforms define timeval as Int/Int
-  self.init(tv_sec: Int(comps.seconds),
-              tv_usec: Int(comps.attoseconds / 1_000_000_000_000))
+#if os(Linux)
+    // Linux platforms define timeval as Int/Int, except on 32-bit platforms
+    // where _TIME_BITS=64 is defined. Abuse time_t as an alias for the correct
+    // suseconds_t type, as it is not an alias to the 64-bit type on 32-bit
+    // platforms.
+    typealias _Seconds = time_t
+    typealias _Microseconds = time_t
+#else
+    typealias _Seconds = Int
+    typealias _Microseconds = Int // note: was Int32 in release/6.1
+#endif
+    self.init(tv_sec: _Seconds(comps.seconds),
+              tv_usec: _Microseconds(comps.attoseconds / 1_000_000_000_000))
   }
 }