This function enables watchpoints:

 	Function:	IO$_LD_CONTROL

 	P1 = address of watchpt structures
 	P2 = number of watchpt structures
 	P6 = Subfunction: LDIO$K_ENABLE_WATCH

 	The watchpt structure must contain a valid lbn, action,
 	function, flags and returncode.

 	IOSB word 0 = status
 	     longword 1 = current number of watchpoints

 	Errors returned:

 	SS$_ACCVIO	Buffer can not be read
 	SS$_NOPRIV	Action needs ownership of device or CMKRNL
 	SS$_NOCMKRNL	CMKRNL privilege needed for CRASH action
 	SS$_EXBYTLM	Out of BYTLIM quota for watch buffers
 	SS$_DEVREQERR	FILE watchpoint must be on the LD device
 	SS$_ILLBLKNUM	Watchpoint past end of file or end of disk or
 			VBN zero specified for file
 	SS$_BADPARAM	Zero buffer length specified or action out of range
 	SS$_FORMAT	FCB specified in SBK is invalid or file not opened
 			with cathedral windows
 	SS$_INSFMEM	Not enough memory to allocate watchpoint buffer
 	SS$_NORMAL	Successful completion