Declare it somewhere at the global scope. In the 2018 version you supplied me, it was on line 19 of globals.c, just after these 2 lines:
float FRAND(float _x) { return rand(32768) / 32768.0 * _x; }
float frandSmall(float _x) { return rand(32) / 32.0 * _x; } // boal
ref pchar;