Fix joystick (/dev/input/xxx) support on FreeBSD

When switching to CMake, src/joystick/linux/SDL_sysjoystick.c file got
excluded from FreeBSD builds, losing support for /dev/input/xxx devices.

See also: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=279907

CMakeLists.txt

@@ -1732,7 +1732,7 @@ elseif(UNIX AND NOT APPLE AND NOT RISCOS AND NOT HAIKU)
     if(FREEBSD OR NETBSD OR OPENBSD OR BSDI)
       CheckUSBHID()
     endif()
-    if(LINUX AND HAVE_LINUX_INPUT_H AND NOT ANDROID)
+    if((LINUX OR FREEBSD) AND HAVE_LINUX_INPUT_H AND NOT ANDROID)
       set(SDL_JOYSTICK_LINUX 1)
       sdl_glob_sources(
         "${SDL3_SOURCE_DIR}/src/joystick/linux/*.c"