1. Organize and comment on various options that we set.
2. Disable all system dependencies explicitly instead of relying on
auto-detection for some of them.
Previously, only the translations were copied for Android at build time.
The other assets were copied only at configure time.
Replaces Android-specific handling with a general mechanism to override
the build-time assets directory.
libmpq is a much simpler alternative to StormLib for reading MPQ archives.
We use our own fork of libmpq: https://github.com/diasurgical/libmpq
Impact:
* DevilutionX is now a lot more portable. Unlike StormLib, libmpq only
needs platform-specific code for Windows.
* Locks around file access **removed** (instead we duplicate the file descriptor for streamed audio only).
* RAM usage is **300 KiB** lower than StormLib.
* Stripped release linux_x86_64 binary is **32 KiB** smaller.
* Amiga build now hangs instead of crashing.
Gleb Mazovetskiy
Anders Jenbo
staphen