start_command: flush buffers in the WIN32 code path as well

The POSIX code path did The Right Thing already, but we have to do the same
on Windows.

This bug caused failures in t5526-fetch-submodules, where the output of
'git fetch --recurse-submodules' was in the wrong order.
Debugged-by: NJohannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: NJohannes Sixt <j6t@kdbg.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

run-command.c

@@ -194,6 +194,7 @@ int start_command(struct child_process *cmd)
 	}
 
 	trace_argv_printf(cmd->argv, "trace: run_command:");
+	fflush(NULL);
 
 #ifndef WIN32
 {
@@ -201,7 +202,6 @@ int start_command(struct child_process *cmd)
 	if (pipe(notify_pipe))
 		notify_pipe[0] = notify_pipe[1] = -1;
 
-	fflush(NULL);
 	cmd->pid = fork();
 	if (!cmd->pid) {
 		/*