Allow macOS builds to be launched through Steam

See merge request STJr/SRB2!996

Strike null-pointer-arithmetic error in BUFFER_OFFSET

See merge request STJr/SRB2!989

Fix OPENMPT deprecation error, openmpt_module_ctl_set

See merge request STJr/SRB2!990

Cppcheck fixes

See merge request STJr/SRB2!967

sdl/i_main.c: while we're here, split all the logging initialisation code into a separate function, to make main function more clean

(though that said we don't officially care about the win32 folder files anymore)

V_Init: count to NUMSCREENS, not NUMSCREENS+1 (though I can't help thinking this one might have been deliberate somehow?)

Polyobj_rotate and related: change "origin" to vector2_t since all it needs is x/y and not any of the new stuff for vertex_t

This way, if for some reason the ghost has no skin, nothing should spawn at all

NOWIPE fixes for colormap and title card wipes

See merge request STJr/SRB2!962

Fix window icon being reset when switching renderers on non-Windows platforms

See merge request STJr/SRB2!898

Fix OpenGL only recording the first frame of unoptimized GIFs

See merge request STJr/SRB2!928

GCC 10 compiling fixes

See merge request STJr/SRB2!937

added missing extern keyword for ms_RoomId in mserv.h (the definition is already in the .c file in this case)

turn all non-extern variables in s_sound.h into externs (and put their real definitions in the .c file)

Fix splitscreen Title Card act name regression

See merge request STJr/SRB2!934

Menu soc bullshit mergefix

See merge request STJr/SRB2!933

2.2.4 preparation

See merge request STJr/SRB2!935

Fix crash with rollout rock

See merge request STJr/SRB2!936

This fixes act names not being shown on player 2's view