riscos: Implement SDL_GetPrefPath()

configure.ac

@@ -4277,6 +4277,12 @@ case "$host" in
         SOURCES="$SOURCES $srcdir/src/misc/riscos/*.c"
         have_misc=yes
 
+        # Set up files for the filesystem library
+        if test x$enable_filesystem = xyes; then
+            AC_DEFINE(SDL_FILESYSTEM_RISCOS, 1, [ ])
+            SOURCES="$SOURCES $srcdir/src/filesystem/riscos/*.c"
+            have_filesystem=yes
+        fi
         # Set up files for the timer library
         if test x$enable_timers = xyes; then
             AC_DEFINE(SDL_TIMER_UNIX, 1, [ ])