Cause more issues than fixes. Still around for Linux.

A and B are v2 terminology

(cherry picked from commit 679bfa21edec6b652def93082da5586e6c755678)

(cherry picked from commit 1f38db46298181d117432e12e88b326a92b4b785)

Attach initial join discord info to servercfg, so that we don't have a pause from needing to also send XD_DISCORD

XD_DISCORD is now reserved for when the options are changed mid-game

- Call DRPC_Init at the end of D_SRB2Main instead of in the middle
- Call Discord_RunCallbacks in D_SRB2Loop instead of G_Ticker
- Fix errorcount nums in I_Error, an old leftover from when Discord_Shutdown was not handled by I_AddExitFunction

Turns out compiling with the internal version of curl was broken on CMake the entire time 

No idea if it compiles on Mac, it does on Linux though, at least for me.