CC Mode: Fix the fontification of a spuriously recognised enum member.

CC Mode: Fix the fontification of a spuriously recognised enum member.

The "enum" was in an argument list, but triggered the fontification of a
following identifier in the function block as though it were in an enum
declaration.

* lisp/progmodes/cc-fonts.el (c-font-lock-enum-body): New function.
(c-basic-matchers-after): Replace the inline stanza for enum elements with a
call to c-font-lock-enum-body.

* lisp/progmodes/cc-langs.el (c-enum-clause-introduction-re): New language
variable.