… both the standard and the modern build. Makefiles still need to be manually switched for each build type.

…er to enable modern build without errors.

…=yes argument. Default is still modern=no for the time being. Using modern setup with legacy build codebase will now error out. Also reverted the :1 bitfield thing since it's now fixed in modern gnustep.

…has no effect on the legacy build, which is very convenient.

… mingw64-msvcrt or clang-ucrt). Just launch the desired dev environment and build the game normally. The makefiles logic can now detect whether to build legacy or modern, based on the gcc version which is available on all environments.

…bjc runtime 2.2 parameter setting.

Hopefully the github runners can build the modern configuration this way.