add defaultObjectTarget to the GHC API

We had no way of getting the right value of HscTarget to use to
request object files as output.

compiler/main/DynFlags.hs

@@ -17,7 +17,7 @@ module DynFlags (
 	-- Dynamic flags
 	DynFlag(..),
 	DynFlags(..),
-	HscTarget(..), isObjectTarget,
+	HscTarget(..), isObjectTarget, defaultObjectTarget,
 	GhcMode(..), isOneShot,
 	GhcLink(..), isNoLink,
 	PackageFlag(..),
@@ -366,7 +366,11 @@ data PackageFlag
   | IgnorePackage  String
   deriving Eq
 
-defaultHscTarget
+defaultHscTarget = defaultObjectTarget
+
+-- | the 'HscTarget' value corresponding to the default way to create
+-- object files on the current platform.
+defaultObjectTarget
   | cGhcWithNativeCodeGen == "YES" 	=  HscAsm
   | otherwise				=  HscC
 

compiler/main/GHC.hs

@@ -15,7 +15,7 @@ module GHC (
 
 	-- * Flags and settings
 	DynFlags(..), DynFlag(..), Severity(..), HscTarget(..), dopt,
-        GhcMode(..), GhcLink(..),
+        GhcMode(..), GhcLink(..), defaultObjectTarget,
 	parseDynamicFlags,
 	getSessionDynFlags,
 	setSessionDynFlags,