Bump Shake and copy instead of hard link from cloud cache

This is important as in hard link mode shake  makes all such files
read only to avoid accidentally modifying cache files via the
hard link. It turns out, many Hadrian rules attempt read access
to such files and hence fail in the hard link mode. These
rules could be refactored to avoid write access, but using
copy instead of hard link a much simpler solution.

hadrian/hadrian.cabal

@@ -128,7 +128,7 @@ executable hadrian
                        , mtl                  == 2.2.*
                        , parsec               >= 3.1     && < 3.2
                        , QuickCheck           >= 2.6     && < 2.13
-                       , shake                >= 0.17.6
+                       , shake                >= 0.18.3
                        , transformers         >= 0.4     && < 0.6
                        , unordered-containers >= 0.2.1   && < 0.3
     build-tools:         alex  >= 3.1

hadrian/src/Main.hs

@@ -41,6 +41,16 @@ main = do
             , shakeTimings  = True
             , shakeExtra    = extra
 
+            -- Setting shakeSymlink to False ensures files are copied out of
+            -- shake's cloud cache instead of hard linked. This is important as
+            -- the hard link mode makes all such files read only to avoid
+            -- accidentally modifying cache files via the hard link. It turns
+            -- out, many Hadrian rules attempt read access to such files and
+            -- hence would in the hard link mode. These rules could be
+            -- refactored to avoid write access, but setting shakeSymlink to
+            -- False is a much simpler solution.
+            , shakeSymlink  = False
+
             -- Enable linting file accesses in the build dir and ghc root dir
             -- (cwd) when using the `--lint-fsatrace` option.
             , shakeLintInside = [ cwd, buildRoot ]