#define MAX_ITEMGROUP 400 ///The max. item group count (increase this when needed). TODO: Remove this limit and use dynamic size or DBMap if needed
They removed this line, because size is loaded dynamically. You can proceed in two ways
Just follow this tutorial but replace the MAX_ITEMGROUP with this method:
1 . Short way
Use db/<re><pre-re>/item_misc.txt
Add your IG group there
Done
2 . Long Way
Open src/map/itemdb.c
look for this lines
sv_readdb(dbsubpath1, "item_avail.txt", ',', 2, 2, -1, &itemdb_read_itemavail, i);
sv_readdb(dbsubpath1, "item_stack.txt", ',', 3, 3, -1, &itemdb_read_stack, i);
sv_readdb(dbsubpath1, "item_nouse.txt", ',', 3, 3, -1, &itemdb_read_nouse, i);
sv_readdb(dbsubpath2, "item_group_db.txt", ',', 2, 10, -1, &itemdb_read_group, i);
sv_readdb(dbsubpath2, "item_bluebox.txt", ',', 2, 10, -1, &itemdb_read_group, i);
sv_readdb(dbsubpath2, "item_violetbox.txt", ',', 2, 10, -1, &itemdb_read_group, i);
sv_readdb(dbsubpath2, "item_cardalbum.txt", ',', 2, 10, -1, &itemdb_read_group, i);
sv_readdb(dbsubpath1, "item_findingore.txt", ',', 2, 10, -1, &itemdb_read_group, i);
sv_readdb(dbsubpath2, "item_giftbox.txt", ',', 2, 10, -1, &itemdb_read_group, i);
sv_readdb(dbsubpath2, "item_misc.txt", ',', 2, 10, -1, &itemdb_read_group, i);
and add your own db, recompile and thats it (not tested)