[Agda] Patch for compilation with GHC-7

[kahl at cas.mcmaster.ca]

 > It seems as if Cabal hardcodes -agc when GHC is used.

I consider that a bug and will try to report it.
(My first attempt was to add ``happy-options: -ag''
to Agda.cabal, but it didn't like that.

 > However, you can run Happy manually

Of course --- I just thought that this should be automatable,
and configurable once and for all...


Thank you!


Are you aware of any other suspicious corners of Agda?
(unsafeCoerce or FFI)
Of course it links with haskeline, but I don't think this could
possibly be an issue in non-interactive agda runs.


Wolfram