driver: fix getGccSearchDirectory for wasm target

This commit fixes getGccSearchDirectory logic for wasm target, ensures
the correct search directory containing libc.so etc can be found by
GHC. getGccSearchDirectory is also exported so it can be used
elsewhere to obtain the wasi-sdk libdir and pass to the dyld script.

(cherry picked from commit b562e3a6)

compiler/GHC/Linker/Loader.hs

@@ -33,6 +33,7 @@ module GHC.Linker.Loader
    , modifyLoaderState
    , initLinkDepsOpts
    , partitionLinkable
+   , getGccSearchDirectory
    )
 where
 
@@ -1491,12 +1492,11 @@ searchForLibUsingGcc logger dflags so dirs = do
 --   libraries and components. See Note [Fork/Exec Windows].
 getGCCPaths :: Logger -> DynFlags -> OS -> IO [FilePath]
 getGCCPaths logger dflags os
-  = case os of
-      OSMinGW32 ->
+  | os == OSMinGW32 || platformArch (targetPlatform dflags) == ArchWasm32 =
         do gcc_dirs <- getGccSearchDirectory logger dflags "libraries"
            sys_dirs <- getSystemDirectories
            return $ nub $ gcc_dirs ++ sys_dirs
-      _         -> return []
+  | otherwise = return []
 
 -- | Cache for the GCC search directories as this can't easily change
 --   during an invocation of GHC. (Maybe with some env. variable but we'll)
@@ -1529,7 +1529,7 @@ getGccSearchDirectory logger dflags key = do
                   modifyIORef' gccSearchDirCache ((key, dirs):)
                   return val
       where split :: FilePath -> [FilePath]
-            split r = case break (==';') r of
+            split r = case break (`elem` [';', ':']) r of
                         (s, []    ) -> [s]
                         (s, (_:xs)) -> s : split xs