Change build product rule signature

[kaoskorobase]

Change signature of build rules in Shake.Development.Language.C.Rules to

buildProduct ::
   Action ToolChain -- ^ Action returning a target 'ToolChain'
-> Action (BuildFlags -> BuildFlags) -- ^ Action returning a 'BuildFlags' modifier
-> Action [FilePath] -- ^ Action returning a list of input source files
-> Rules (FilePath -> Action()) -- ^ Rule returning an action that produces the given output file

This would allow for further build product processing without introducing intermediate (phony) targets. The old rules functions can still be provided as trivial wrappers of the new ones:

buildProcuct_ toolChain flags sources output =
  (output *>) =<< buildProduct toolChain flags sources