.. except where SDL_Swap* is actually used (idlib/Lib.cpp).
Otherwise #if D3_IS_BIG_ENDIAN suffices, (NOT #ifdef, it's always set,
but to either 0 or 1!)
the stb libs, miniz and minizip are now always optimized to speed up
performance, esp. level loading times, in debug builds.
So far the stb libs implementation were dragged into the source file
that uses them, now I created additional source files just for them so
those can be optimized while the engine source files using those libs
can remain unoptimized in debug builds.