illumos gate

During #15891 I discovered that

      == 

where there should be non-empty strings on both sides but instead both are empty, count as success.

My RTI advocate for 15891 suggested I file a bug here, so I am. As with 15891, it may expose architectural issues that OpenZFS should be made aware of, as well.

These tests were thought to be completely broken with 15891, but instead showed THIS issue. There may be more.

nowhere(test/zfs-tests)[0]% git grep -lw digest | fgrep .ksh
tests/functional/cli_root/zfs_receive/zfs_receive_from_encrypted.ksh
tests/functional/cli_root/zfs_receive/zfs_receive_raw.ksh
tests/functional/cli_root/zfs_receive/zfs_receive_raw_incremental.ksh
tests/functional/history/history_003_pos.ksh
tests/functional/rsend/send-c_volume.ksh
tests/functional/rsend/send-wDR_encrypted_zvol.ksh
tests/functional/rsend/send_encrypted_props.ksh
nowhere(test/zfs-tests)[0]%