CC Mode: fix c-where-wrt-brace-construct to cope with class declarations

CC Mode: fix c-where-wrt-brace-construct to cope with class declarations

Make the function correctly recognize a brace block preceded by an
introductory line without a parameter list.

* lisp/progmodes/cc-cmds.el (c-where-wrt-brace-contruct): Reintroduce the use
of c-beginning-of-decl-1, which was removed some weeks ago, in place of a
c-syntactic-skip-backward.  Reformulate the code generally.