INT 21 - DOS 3.x+ internal - GET AND SET EXTENDED CONTROL-BREAK CHECKING STATE
AX = 3302h
DL = new state
00h for OFF or 01h for ON
Return: DL = old state of extended BREAK checking
Note:   this function does not use any of the DOS-internal stacks and may thus
be called at any time; one possible use is modifying Control-Break
checking from within an interrupt handler or TSR

See also: 2133

213302 - DOS 3.x+ internal - GET AND SET EXTENDED CONTROL-BREAK CHECKING STATE