better runtime options for GHC 7.8.

-A32m: heap size should be 32m rather than 4m.
-qa: each IO manager does not move from its core.
-N: use all cores.
Other GC options are removed.

For more information, see:
- https://github.com/yesodweb/wai/issues/246
- https://github.com/TechEmpower/FrameworkBenchmarks/issues/829
- https://github.com/TechEmpower/FrameworkBenchmarks/issues/830