Condition runST import in Data/Primitive/Array.hs

runST is not used in this file on GHC 7.0.2 and higher, hence importing
it from Control.Monad.ST produces a warning during compilation.  This
commit makes the warning go away.
The actual usage of `runST` later in the file occurs in an `#else` block, where the condition is `__GLASGOW_HASKELL__ >= 702`. Thus `!(__GLASGOW_HASKELL__ >= 702)` is the most precise description of under what conditions `runST` will be needed. I wasn't sure about the semantics of the preprocessor when, for example, `__GLASGOW_HASKELL__` was not defined, or was not a number, or was not a number comparable to `702`.