Fix Pipe Inheritance on Windows

- The Security Attributes should allow handle inheritance
- The Startup info should indicate the child should use the passed in
  pipes for stdin/stdout/stderr
- The write end of stdin and read end of stdout/stderr shouldn't be
  inherited by the child

Author: gmittert

Foundation/FileHandle.swift

@@ -975,9 +975,15 @@ open class Pipe: NSObject {
 
     public override init() {
 #if os(Windows)
+        var saAttr = SECURITY_ATTRIBUTES()
+        saAttr.nLength = DWORD(MemoryLayout<SECURITY_ATTRIBUTES>.size)
+        saAttr.bInheritHandle = true
+        saAttr.lpSecurityDescriptor = nil
+
         var hReadPipe: HANDLE?
         var hWritePipe: HANDLE?
-        if !CreatePipe(&hReadPipe, &hWritePipe, nil, 0) {
+
+        if !CreatePipe(&hReadPipe, &hWritePipe, &saAttr, 0) {
           fatalError("CreatePipe failed")
         }
         self.fileHandleForReading = FileHandle(handle: hReadPipe!,

Foundation/Process.swift

@@ -386,6 +386,7 @@ open class Process: NSObject {
 
         var siStartupInfo: STARTUPINFOW = STARTUPINFOW()
         siStartupInfo.cb = DWORD(MemoryLayout<STARTUPINFOW>.size)
+        siStartupInfo.dwFlags = DWORD(STARTF_USESTDHANDLES)
 
         var _devNull: FileHandle?
         func devNullFd() throws -> HANDLE {
@@ -396,6 +397,7 @@ open class Process: NSObject {
         switch standardInput {
         case let pipe as Pipe:
             siStartupInfo.hStdInput = pipe.fileHandleForReading.handle
+            SetHandleInformation(pipe.fileHandleForWriting.handle, DWORD(HANDLE_FLAG_INHERIT), 0)
 
         // nil or NullDevice maps to NUL
         case let handle as FileHandle where handle === FileHandle._nulldeviceFileHandle: fallthrough
@@ -410,6 +412,7 @@ open class Process: NSObject {
         switch standardOutput {
         case let pipe as Pipe:
             siStartupInfo.hStdOutput = pipe.fileHandleForWriting.handle
+            SetHandleInformation(pipe.fileHandleForReading.handle, DWORD(HANDLE_FLAG_INHERIT), 0)
 
         // nil or NullDevice maps to NUL
         case let handle as FileHandle where handle === FileHandle._nulldeviceFileHandle: fallthrough
@@ -424,6 +427,7 @@ open class Process: NSObject {
         switch standardError {
         case let pipe as Pipe:
             siStartupInfo.hStdError = pipe.fileHandleForWriting.handle
+            SetHandleInformation(pipe.fileHandleForReading.handle, DWORD(HANDLE_FLAG_INHERIT), 0)
 
         // nil or NullDevice maps to NUL
         case let handle as FileHandle where handle === FileHandle._nulldeviceFileHandle: fallthrough