AP_Filesystem: Split the available define to it's own header

libraries/AP_Filesystem/AP_Filesystem.h

@@ -22,11 +22,7 @@
 #include <stdint.h>
 #include <AP_HAL/AP_HAL_Boards.h>
 
-#if HAL_OS_POSIX_IO || HAL_OS_FATFS_IO
-#define HAVE_FILESYSTEM_SUPPORT 1
-#else
-#define HAVE_FILESYSTEM_SUPPORT 0
-#endif
+#include "AP_Filesystem_Available.h"
 
 #if HAVE_FILESYSTEM_SUPPORT
 #if CONFIG_HAL_BOARD == HAL_BOARD_CHIBIOS

libraries/AP_Filesystem/AP_Filesystem_Available.h

@@ -0,0 +1,26 @@
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+// minimal header for checking if AP_FS is available
+
+#pragma once
+
+#include <AP_HAL/AP_HAL_Boards.h>
+
+#if HAL_OS_POSIX_IO || HAL_OS_FATFS_IO
+#define HAVE_FILESYSTEM_SUPPORT 1
+#else
+#define HAVE_FILESYSTEM_SUPPORT 0
+#endif