waitUntilExit: ignore RunLoop.run()'s return value (#4740)

* waitUntilExit: ignore RunLoop.run()'s return value

We've been seeing frequent (but not reproducible in isolation) failures
in our builds where waitUntilExit returns but terminationStatus fails
its precondition on hasFinished because isRunning is still true.
This is a speculative fix, since I haven't been able to reproduce the
failure in a self-contained test.

This should be safe since Process.waitUntilExit isn't spec'd to relate
to RunLoop. In particular there is no guarantee that "stopping" a
RunLoop should cause waitUntilExit to return before the monitored
process has exited.

* Exclude libdispatch_init() on TARGET_OS_MAC because it duplicates the call from the static constructor https://github.com/apple/swift-corelibs-libdispatch/blob/7fb9d5ceea562d60fe34ec55b6b165ae5aca38eb/src/init.c#L56

(cherry picked from commit 818de48)

Author: fischman-bcny

CoreFoundation/Base.subproj/CFRuntime.c

@@ -1179,7 +1179,7 @@ void __CFInitialize(void) {
     if (!__CFInitialized && !__CFInitializing) {
         __CFInitializing = 1;
 
-#if __HAS_DISPATCH__
+#if __HAS_DISPATCH__ && !TARGET_OS_MAC
     // libdispatch has to be initialized before CoreFoundation, so to avoid
     // issues with static initializer ordering, we are doing it explicitly.
     libdispatch_init();

Sources/Foundation/Process.swift

@@ -1134,14 +1134,17 @@ open class Process: NSObject {
     open func waitUntilExit() {
         let runInterval = 0.05
         let currentRunLoop = RunLoop.current
-        let checkRunLoop : () -> Bool = (currentRunLoop == self.runLoop)
-                ? { currentRunLoop.run(mode: .default, before: Date(timeIntervalSinceNow: runInterval)) }
-                : { currentRunLoop.run(until: Date(timeIntervalSinceNow: runInterval)); return true }
 
-        // update .runLoop to allow early wakeup.
+        let runRunLoop : () -> Void = (currentRunLoop == self.runLoop)
+                ? { currentRunLoop.run(mode: .default, before: Date(timeIntervalSinceNow: runInterval)) }
+                : { currentRunLoop.run(until: Date(timeIntervalSinceNow: runInterval)) }
+        // update .runLoop to allow early wakeup triggered by terminateRunLoop.
         self.runLoop = currentRunLoop
-        while self.isRunning && checkRunLoop() {}
-        
+
+        while self.isRunning {
+            runRunLoop()
+        } 
+
         self.runLoop = nil
         self.runLoopSource = nil
     }