Fix Windows GCC driver

In Windows 10 Insiders build 15019+ which will probably be released
mainstream somewhere this year Microsoft seems to have started being
stricter with API calls.

The call to `FreeConsole` just after `CreateProcess` is making Windows
treat the process
as an interactive process. In which case it tries to use the `Desktop
session` but fails resulting
in the cryptic error reported.

I don't understand why the call to `FreeConsole` was there and it
doesn't seem to be needed,
so removed.

This fixes #13411

Test Plan: ./validate, alternative just do anything with ghc which
requires compilation.

Reviewers: austin, bgamari, simonmar

Reviewed By: bgamari

Subscribers: rwbarton, thomie, #ghc_windows_task_force

Differential Revision: https://phabricator.haskell.org/D3319

driver/utils/cwrapper.c

@@ -130,11 +130,9 @@ __attribute__((noreturn)) int run (char *exePath,
                        &pi) ) {
         die("Unable to start %s (error code: %lu)\n", exePath, GetLastError());
     }
-    /* Disable handling of console events in the parent by dropping its
-     * connection to the console. This has the (minor) downside of not being
-     * able to subsequently emit any error messages to the console.
-     */
-    FreeConsole();
+
+    /* Synchronize input and wait for target to be ready.  */
+    WaitForInputIdle(pi.hProcess, INFINITE);
 
     switch (WaitForSingleObject(pi.hProcess, INFINITE) ) {
     case WAIT_OBJECT_0: