Fix fontification of "operator~" in C++ Mode.

Fix fontification of "operator~" in C++ Mode.

* lisp/progmodes/cc-langs.el (c-ambiguous-overloadable-or-identifier-prefices)
(c-ambiguous-overloadable-or-identifier-prefix-re): New c-lang-defconsts/vars.

* lisp/progmodes/cc-engine.el (c-forward-name): Do not try to parse "~" (and
two other symbols) as a cast without good evidence.  Prefer an overloaded
operator in ambiguous cases.