Require PHP 7.4 at least for running the build system

[kocsismate]

Due to #9512 (comment). The target branch (PHP-8.2 vs master) can be under debate, but I chose the former for now.

I guess our Travis config should be adapted as well in order to use PHP 7.4, but I'm not sure yet how to do (will have time later to find it out)

[iluuu1994]

Pretty gross but this would work 😜

<?php

if (PHP_VERSION_ID < 70400) {
    throw new Exception("The build system requires PHP 7.4 at least.\n");
}

$file = file_get_contents(__FILE__);
eval(explode('__halt_compiler();', $file, 3)[2]);

__halt_compiler();

// Unsupported syntax

[kocsismate]

Pretty gross but this would work

Ilija.... 😂 Actually, this is madly brilliant, but I hope that you won't be upset if I don't use it (?).

[iluuu1994]

I'm incredibly disappointed but I'll be ok 😂