tools/c2hs: Parse __int128 and friends as "int"

This is a hack, but all we really want to do is ignore them for now.

See https://bugzilla.gnome.org/show_bug.cgi?id=699722
Merge pull request #18 from cjwatson/aarch64-int128

tools/c2hs: Parse __int128 and friends as "int"