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

Backport f8ad4abe from main branch.

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
and: https://github.com/libsdl-org/SDL/pull/10087

CMakeLists.txt

@@ -1675,7 +1675,7 @@ 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)
       file(GLOB JOYSTICK_SOURCES ${SDL2_SOURCE_DIR}/src/joystick/linux/*.c ${SDL2_SOURCE_DIR}/src/joystick/steam/*.c)
       list(APPEND SOURCE_FILES ${JOYSTICK_SOURCES})