On error Jlink exits with a no error code by default.
From the JLink User Guide:
'-ExitOnError' has the same meaning as the 'exitonerror' command
'exitonerror' command
This command toggles whether J-Link Commander exits on error or not.
1: J-Link Commander will now exit on Error.
0: J-Link Commander will no longer exit on Error.
Executing 'flash/reset' without a board connected now correctly returns an
error. For 'term' it does not show an error due to the way it is handled
internally.
It also returns an error when the board fails to do an operation when it
is in a state where it cannot be flashed for example.
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