OS/2: Include unistd.h in modules/access_output/files.c

Thie fixes the following error.

-----
make.exe[1]: Entering directory `F:/lang/work/vlc/vlc.git/modules/access_output'
  CC     libaccess_output_file_plugin_la-file.lo
file.c: In function 'Open':
file.c:142: error: 'STDOUT_FILENO' undeclared (first use in this function)
file.c:142: error: (Each undeclared identifier is reported only once
file.c:142: error: for each function it appears in.)
make.exe[1]: *** [libaccess_output_file_plugin_la-file.lo] Error 1
make.exe[1]: Leaving directory `F:/lang/work/vlc/vlc.git/modules/access_output'
make.exe: *** [all] Error 2
-----
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

modules/access_output/file.c

@@ -44,7 +44,9 @@
 
 #if defined( WIN32 ) || defined( __OS2__ )
 #   include <io.h>
-#else
+#endif
+
+#ifndef WIN32
 #   include <unistd.h>
 #endif