c-line-comment-starter

c-line-comment-starter is a variable defined in `cc-engine.el'.
Its value is

nil

• Automatically becomes buffer-local when set.

Documentation:
String that starts line comments, or nil if such don't exist.
Line comments are always terminated by newlines. At least one of
`c-block-comment-starter' and this one is assumed to be set.

Note that it's currently not enough to set this to support a new
comment style. Other stuff like the syntax table must also be set up
properly.