updater: add include guard for windows process start code

Change-Id: If021a92163381f2221faa1c7121f6c4af2d51dcf
Reviewed-on: https://gerrit.libreoffice.org/40836Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

onlineupdate/inc/winhelper/windowsStart.hxx

@@ -3,6 +3,9 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#ifndef INCLUDED_ONLINEUPDATE_INC_WINSTART_HXX
+#define INCLUDED_ONLINEUPDATE_INC_WINSTART_HXX
+
 #ifdef _WIN32
 #include <windows.h>
 #endif
@@ -19,3 +22,5 @@ WinLaunchChild(const wchar_t *exePath, int argc,
                HANDLE *hProcess = nullptr);
 
 wchar_t* MakeCommandLine(int argc, WCHAR **argv);
+
+#endif