Don't perform unaligned writes

Some architectures, such as SPARC, trap on unaligned memory accesses,
and poke makes no guarantees about its behaviour if the address is not
sufficiently aligned. Therefore we should use a temporary buffer if
asked to write to an unaligned address.

Data/ByteString/Builder/Prim/Internal.hs

@@ -198,7 +198,9 @@ liftFixedToBounded = toB
 
 {-# INLINE CONLIKE storableToF #-}
 storableToF :: forall a. Storable a => FixedPrim a
-storableToF = FP (sizeOf (undefined :: a)) (\x op -> poke (castPtr op) x)
+storableToF = FP (sizeOf (undefined :: a)) $ \x op ->
+    if (ptrToWordPtr op) `mod` (fromIntegral (alignment (undefined :: a))) == 0 then poke (castPtr op) x
+    else with x $ \tp -> copyBytes op (castPtr tp) (sizeOf (undefined :: a))
 
 {-
 {-# INLINE CONLIKE liftIOF #-}