cwarn-font-lock-feature-keywords-alist is a variable defined in `cwarn.el'.
Its value is

((assign . cwarn-font-lock-assignment-keywords) (semicolon . cwarn-font-lock-semicolon-keywords) (reference . cwarn-font-lock-reference-keywords))

An alist mapping a CWarn feature to font-lock keywords.
The keywords could either a font-lock keyword list or a symbol.
If it is a symbol it is assumed to be a variable containing a font-lock
keyword list.

You can customize this variable.