c-make-keywords-re is a compiled Lisp function in `cc-defs.el'.

(c-make-keywords-re ADORN LIST &optional MODE)

Make a regexp that matches all the strings the list.
Duplicates and nil elements in the list are removed. The
resulting regexp may contain zero or more submatch expressions.

If ADORN is t there will be at least one submatch and the first
surrounds the matched alternative, and the regexp will also not match
a prefix of any identifier. Adorned regexps cannot be appended. The
language variable `c-nonsymbol-key' is used to make the adornment.

A value 'appendable for ADORN is like above, but all alternatives in
the list that end with a word constituent char will have \> appended
instead, so that the regexp remains appendable. Note that this
variant doesn't always guarantee that an identifier prefix isn't
matched since the symbol constituent '_' is normally considered a
nonword token by \>.

The optional MODE specifies the language to get `c-nonsymbol-key' from
when it's needed. The default is the current language taken from