* demangle.c (is_cplus_marker): New function, checks if a
character is one of the commonly used C++ marker characters.
* defs.h (is_cplus_marker): Add prototype.
* c-typeprint.c (c_type_print_base), ch-lang.c (chill_demangle),
cp-valprint.c (cp_print_class_method), mdebugread.c (parse_symbol),
stabsread.c (define_symbol, read_member_functions, read_struct_fields),
symtab.h (OPNAME_PREFIX_P, VTBL_PREFIX_P, DESTRUCTOR_PREFIX_P),
values.c (vb_match): Use is_cplus_marker instead of comparison
with CPLUS_MARKER.