Disable benchmarks for old GHC

Author: Shimuuar

math-functions.cabal

@@ -130,6 +130,8 @@ test-suite math-function-tests
 
 benchmark math-functions-bench
  type: exitcode-stdio-1.0
+ if impl(ghc <= 7.10 ) || impl(ghcjs)
+ buildable: False
  default-language: Haskell2010
  other-extensions:
  BangPatterns