Compatibility: 2.0+
Expects: AH    4dH
Returns: AL    exit code  of last process to terminate
AH    Exit method: 0 = normal termination
1 = Ctrl-Break termination  INT 23H
2 = termination via critical error  INT 24H
3 = termination via Fn 31H KEEP
Info: Returns the exit code of the most-recently terminated process.
The exit code is set when a program calls DOS Fn 4cH or 31H.

This function returns valid information only once for each
terminating process.

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DOS Fn 4dH: Get Program Exit Code