Fix compilation on modern Linux systems

[unrealtournament]

I was trying to compile the master branch on Ubuntu 24.04 and GCC 13, and I got a bunch of missing include or library errors. This PR makes it compile properly on modern systems. For reference, in case it helps anyone, here are compilation instructions for Ubuntu 22.04/24.04:

apt-get update && apt-get install -y build-essential cmake automake libsdl2-dev libsdl2-image-dev libsdl2-ttf-dev libsdl2-mixer-dev libxerces-c-dev libenet-dev xdg-utils libpng-dev zlib1g-dev git gettext libcurl4-openssl-dev
git clone https://github.com/unrealtournament/Enigma
cd Enigma

mkdir build && cd build
cmake ..
make

You could also compile this on a Docker container and then copy it to the host, the libraries required (on the host) to run it are:

sudo apt-get update && sudo apt-get install -y fonts-dejavu-extra libenet7 libfluidsynth3 libinstpatch-1.0-2 libmodplug1 libopusfile0 libsdl2-image-2.0-0 libsdl2-mixer-2.0-0 fluid-soundfont-gm libsdl2-2.0-0 libsdl2-ttf-2.0-0 libxerces-c3.2t64

To run it afterwards, make sure to pass the proper parameters (this assumes current directory as the repo base dir):

./build/src/enigma --data data/ --l10n data/locale/