Return a coding system which differs from CODING-SYSTEM in EOL conversion.
The returned coding system converts end-of-line by EOL-TYPE
but text as the same way as CODING-SYSTEM.
EOL-TYPE should be `unix', `dos', `mac', or nil.
If EOL-TYPE is nil, the returned coding system detects
how end-of-line is formatted automatically while decoding.
EOL-TYPE can be specified by an integer 0, 1, or 2.
They means `unix', `dos', and `mac' respectively.