update sdl2 to release https://github.com/spurious/SDL-mirror/tree/release-2.0.14

Engine/lib/sdl/docs/README-linux.md

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+Linux
+================================================================================
+
+By default SDL will only link against glibc, the rest of the features will be
+enabled dynamically at runtime depending on the available features on the target
+system. So, for example if you built SDL with Xinerama support and the target
+system does not have the Xinerama libraries installed, it will be disabled
+at runtime, and you won't get a missing library error, at least with the 
+default configuration parameters.
+
+
+================================================================================
+Build Dependencies
+================================================================================
+    
+Ubuntu 20.04, all available features enabled:
+
+sudo apt-get install build-essential mercurial make cmake autoconf automake \
+libtool libasound2-dev libpulse-dev libaudio-dev libx11-dev libxext-dev \
+libxrandr-dev libxcursor-dev libxi-dev libxinerama-dev libxxf86vm-dev \
+libxss-dev libgl1-mesa-dev libdbus-1-dev libudev-dev libgles2-mesa-dev \
+libegl1-mesa-dev libibus-1.0-dev fcitx-libs-dev libsamplerate0-dev \
+libsndio-dev libwayland-dev libxkbcommon-dev
+
+NOTES:
+- This includes all the audio targets except arts and esd, because Ubuntu
+  (and/or Debian) pulled their packages, but in theory SDL still supports them.
+- libsamplerate0-dev lets SDL optionally link to libresamplerate at runtime
+  for higher-quality audio resampling. SDL will work without it if the library
+  is missing, so it's safe to build in support even if the end user doesn't
+  have this library installed.
+- DirectFB isn't included because the configure script (currently) fails to find
+  it at all. You can do "sudo apt-get install libdirectfb-dev" and fix the 
+  configure script to include DirectFB support. Send patches.  :)
+
+
+================================================================================
+Joystick does not work
+================================================================================
+
+If you compiled or are using a version of SDL with udev support (and you should!)
+there's a few issues that may cause SDL to fail to detect your joystick. To
+debug this, start by installing the evtest utility. On Ubuntu/Debian:
+
+    sudo apt-get install evtest
+    
+Then run:
+    
+    sudo evtest
+    
+You'll hopefully see your joystick listed along with a name like "/dev/input/eventXX"
+Now run:
+    
+    cat /dev/input/event/XX
+
+If you get a permission error, you need to set a udev rule to change the mode of
+your device (see below)    
+    
+Also, try:
+    
+    sudo udevadm info --query=all --name=input/eventXX
+    
+If you see a line stating ID_INPUT_JOYSTICK=1, great, if you don't see it,
+you need to set up an udev rule to force this variable.
+
+A combined rule for the Saitek Pro Flight Rudder Pedals to fix both issues looks 
+like:
+    
+   SUBSYSTEM=="input", ATTRS{idProduct}=="0763", ATTRS{idVendor}=="06a3", MODE="0666", ENV{ID_INPUT_JOYSTICK}="1"
+   SUBSYSTEM=="input", ATTRS{idProduct}=="0764", ATTRS{idVendor}=="06a3", MODE="0666", ENV{ID_INPUT_JOYSTICK}="1"
+   
+You can set up similar rules for your device by changing the values listed in
+idProduct and idVendor. To obtain these values, try:
+    
+    sudo udevadm info -a --name=input/eventXX | grep idVendor
+    sudo udevadm info -a --name=input/eventXX | grep idProduct
+    
+If multiple values come up for each of these, the one you want is the first one of each.    
+
+On other systems which ship with an older udev (such as CentOS), you may need
+to set up a rule such as:
+    
+    SUBSYSTEM=="input", ENV{ID_CLASS}=="joystick", ENV{ID_INPUT_JOYSTICK}="1"
+