[patch] change specific int128 -> generic intN

[DJ Delorie]

So I'm still working on macro-izing the C++ headers, and I ran into this error:

.../msp430-elf/large/libstdc++-v3/include/bits/istream.tcc:522:16: error: '__max' is not a member of '__gnu_cxx::__numeric_traits<__int20>'
     if (__n == __gnu_cxx::__numeric_traits<streamsize>::__max
                ^

I can't figure out how to fix this.  I added __int20 to
std::numeric_traits, and it returns true for is_integer, so it should
act like all the other integer types, and I can't see anything in
__gnu_cxx::__numeric_traits that has a "list of all types" to add
__int20 to.

Ideas?