bpo-32560: inherit the py launcher's STARTUPINFO (GH-9000)

https://bugs.python.org/issue32560

Misc/NEWS.d/next/Windows/2019-02-02-11-02-44.bpo-32560.I5WAGW.rst

@@ -0,0 +1,2 @@
+The ``py`` launcher now forwards its ``STARTUPINFO`` structure to child
+processes.

PC/launcher.c

@@ -666,7 +666,7 @@ run_child(wchar_t * cmdline)
     if (!ok)
         error(RC_CREATE_PROCESS, L"Job information setting failed");
     memset(&si, 0, sizeof(si));
-    si.cb = sizeof(si);
+    GetStartupInfoW(&si);
     ok = safe_duplicate_handle(GetStdHandle(STD_INPUT_HANDLE), &si.hStdInput);
     if (!ok)
         error(RC_NO_STD_HANDLES, L"stdin duplication failed");