This is part of Win16 API which allow to create versions of program from one source code to run under OS/2 and Win16. Under OS/2 program can be running under Win-OS/2 if program is Windows NE executable, and with help on Windows Libraries for OS/2, if it is OS/2 NE executable. Here is a WLO to OS/2 API mapping draft
void WINAPI FatalExit(int nErrCode);
int nErrCode - error code
None
The FatalExit() function displays the error code nErrCode in the debugger and halts execution. If the debugger is running, the user can terminate the application or continue. If the debugger is not running, the application is terminated.