L4: GCC 4.9 compatibility of libstdc++-headers

Just copied this one from 4.8 as I don't know where to get them from.
L4: GCC 4.9 compatibility of libstdc++

Copied from GCC source tree and added 4.9
L4: GCC 4.9 compatibility for libsupc++

Just copied from 4.8, I am not sure how the files are selected as
there are much more.