Don't prematurely link shared libraries against the RTS package

We want to be able to pick the RTS flavour (e.g. -threaded) when we
link the final program.

compiler/main/DriverPipeline.hs

@@ -1433,13 +1433,19 @@ linkDynLib dflags o_files dep_packages = do
     let verb = getVerbFlag dflags
     let o_file = outputFile dflags
 
-    pkg_lib_paths <- getPackageLibraryPath dflags dep_packages
+    -- We don't want to link our dynamic libs against the RTS package,
+    -- because the RTS lib comes in several flavours and we want to be
+    -- able to pick the flavour when a binary is linked.
+    pkgs <- getPreloadPackagesAnd dflags dep_packages
+    let pkgs_no_rts = filter ((/= rtsPackageId) . packageConfigId) pkgs
+
+    let pkg_lib_paths = collectLibraryPaths pkgs_no_rts
     let pkg_lib_path_opts = map ("-L"++) pkg_lib_paths
 
     let lib_paths = libraryPaths dflags
     let lib_path_opts = map ("-L"++) lib_paths
 
-    pkg_link_opts <- getPackageLinkOpts dflags dep_packages
+    let pkg_link_opts = collectLinkOpts dflags pkgs_no_rts
 
 	-- probably _stub.o files
     extra_ld_inputs <- readIORef v_Ld_inputs

compiler/main/Packages.lhs

@@ -26,6 +26,8 @@ module Packages (
 	getPackageFrameworks,
 	getPreloadPackagesAnd,
 
+        collectIncludeDirs, collectLibraryPaths, collectLinkOpts,
+
 	-- * Utils
 	isDllName
     )
@@ -604,21 +606,29 @@ pprPkg p = text (display (package p))
 -- use.
 
 getPackageIncludePath :: DynFlags -> [PackageId] -> IO [String]
-getPackageIncludePath dflags pkgs = do
-  ps <- getPreloadPackagesAnd dflags pkgs
-  return (nub (filter notNull (concatMap includeDirs ps)))
+getPackageIncludePath dflags pkgs =
+  collectIncludeDirs `fmap` getPreloadPackagesAnd dflags pkgs
+
+collectIncludeDirs :: [PackageConfig] -> [FilePath] 
+collectIncludeDirs ps = nub (filter notNull (concatMap includeDirs ps))
 
 getPackageLibraryPath :: DynFlags -> [PackageId] -> IO [String]
-getPackageLibraryPath dflags pkgs = do 
-  ps <- getPreloadPackagesAnd dflags pkgs
-  return (nub (filter notNull (concatMap libraryDirs ps)))
+getPackageLibraryPath dflags pkgs =
+  collectLibraryPaths `fmap` getPreloadPackagesAnd dflags pkgs
+
+collectLibraryPaths :: [PackageConfig] -> [FilePath]
+collectLibraryPaths ps = nub (filter notNull (concatMap libraryDirs ps))
 
 getPackageLinkOpts :: DynFlags -> [PackageId] -> IO [String]
-getPackageLinkOpts dflags pkgs = do
-  ps <- getPreloadPackagesAnd dflags pkgs
-  let tag = buildTag dflags
-      rts_tag = rtsBuildTag dflags
-  let 
+getPackageLinkOpts dflags pkgs = 
+  collectLinkOpts dflags `fmap` getPreloadPackagesAnd dflags pkgs
+
+collectLinkOpts :: DynFlags -> [PackageConfig] -> [String]
+collectLinkOpts dflags ps = concat (map all_opts ps)
+  where
+        tag = buildTag dflags
+        rts_tag = rtsBuildTag dflags
+
 	mkDynName | opt_Static = id
 		  | otherwise = (++ ("-ghc" ++ cProjectVersion))
       	libs p     = map (mkDynName . addSuffix) (hsLibraries p)
@@ -631,8 +641,6 @@ getPackageLinkOpts dflags pkgs = do
         expandTag t | null t = ""
 		    | otherwise = '_':t
 
-  return (concat (map all_opts ps))
-
 getPackageExtraCcOpts :: DynFlags -> [PackageId] -> IO [String]
 getPackageExtraCcOpts dflags pkgs = do
   ps <- getPreloadPackagesAnd dflags pkgs