Loosen bounds on language-c

[vmchale]

c2hs requires language-c >=0.7.1 && <0.9 now, but it could be relaxed to >=0.7.1 && <0.10

This would allow it to build with GHC 9.0, for one!

Thanks :)

[felixonmars]

There is one failing test: https://github.com/haskell/c2hs/pull/261