c++: please G++ 4.8 with -O3: array bounds

c++: please G++ 4.8 with -O3: array bounds

* data/c++.m4, data/lalr1.cc (by_state, by_type): Do not use -1 to
denote the absence of value, as GCC then fears that this -1 might
be used to dereference arrays (such as yytname).
Use 0, which corresponds to $accept, which is valueless (the needed
property: the symbol destructor must not try to reclaim the memory
associated with the symbol).