Correctly fontify C++'s operator"" _tag (...)

Correctly fontify C++'s operator"" _tag (...)

Give both the "" and _tag font-lock-function-name-face.  Also correct the
fontification of an inherited class name when there is an attribute between
the class name being declared and the colon introducing the inheritance.

* lisp/progmodes/cc-engine.el (c-forward-over-colon-type-list): New function.
(c-forward-keyword-clause): Use the above new function instead of a
looking-at.
(c-forward-name, c-forward-declarator): Accept both the "" and the tag as part
of the name.

* lisp/progmodes/cc-fonts.el (c-font-lock-declarators): Fontify the "" (which
already has font-lock-string-face) and the tag with
font-lock-function-name-face.

* lisp/progmodes/cc-langs.el (c-overloadable-operators): Add "" to this list.
(c-sub-colon-type-list-re): New lang-const and lang-var.