re PR objc/23710 (objc front-end should not "abort" after erroring out about method definition not in class context)

PR objc/23710
In gcc/:
        * c-family/c-common.h (objc_start_method_definition): Return bool
        instead of void.
        * c-family/stub-objc.c (objc_start_method_definition): Return bool
        instead of void.
        * c-parser.c (c_parser_objc_method_definition): Check the return
        value of objc_start_method_definition and if false is returned,
        parse the method definition but emit no code.
In gcc/objc/:
        * objc-act.c (objc_start_method_definition): Do not abort upon a
        'method definition not in @implementation context' error.  Return
        'false' instead.
In gcc/testsuite/:
       * objc.dg/invalid-method-1.m: New.

From-SVN: r164497