hadrian: Call ghc-pkg recache after copying package database into bindist

The package.cache needs to have a later mod-time than all of the .conf
files. This invariant can be destroyed by `cp -r` and so we run `ghc-pkg
recache` to ensure the package database which is distributed is
consistent.

If you are installing a relocatable bindist, for example, on windows,
you should preserve mtimes by using cp -a or run ghc-pkg recache after
installing.

(cherry picked from commit 957fe359)

hadrian/src/Rules/BinaryDist.hs

@@ -150,7 +150,14 @@ bindistRules = do
               else createFileLink install_path unversioned_install_path
         copyDirectory (ghcBuildDir -/- "lib") bindistFilesDir
         copyDirectory (rtsIncludeDir)         bindistFilesDir
+
+        -- Call ghc-pkg recache, after copying so the package.cache is
+        -- accurate, then it's on the distributor to use `cp -a` to install
+        -- a relocatable bindist.
+        cmd_ (bindistFilesDir -/- "bin" -/- "ghc-pkg") ["recache"]
+
         need ["docs"]
+
         -- TODO: we should only embed the docs that have been generated
         -- depending on the current settings (flavours' "ghcDocs" field and
         -- "--docs=.." command-line flag)