rWrapper: use symlinkJoin instead of runCommand

While trying to build a haskell-project I got:

Configuring library for inline-r-0.10.4..
cabal: The pkg-config package 'libR' version ==3.0 || >3.0 is required but it
could not be found.

the rWrapper was only bringing the R binary without its companion
library: this fixes it.

pkgs/development/r-modules/wrapper.nix

@@ -1,21 +1,31 @@
-{ runCommand, R, makeWrapper, recommendedPackages, packages }:
-
-runCommand (R.name + "-wrapper") {
+{ symlinkJoin, R, makeWrapper, recommendedPackages, packages }:
+symlinkJoin {
+  name = R.name + "-wrapper";
   preferLocalBuild = true;
   allowSubstitutes = false;
 
   buildInputs = [R] ++ recommendedPackages ++ packages;
+  paths = [ R ];
 
   nativeBuildInputs = [makeWrapper];
 
+  postBuild = ''
+    cd ${R}/bin
+    for exe in *; do
+      rm "$out/bin/$exe"
+
+      makeWrapper "${R}/bin/$exe" "$out/bin/$exe" \
+        --prefix "R_LIBS_SITE" ":" "$R_LIBS_SITE"
+    done
+  '';
+
   # Make the list of recommended R packages accessible to other packages such as rpy2
   passthru = { inherit recommendedPackages; };
+
+    meta = R.meta // {
+      # To prevent builds on hydra
+      hydraPlatforms = [];
+      # prefer wrapper over the package
+      priority = (R.meta.priority or 0) - 1;
+    };
 }
-''
-mkdir -p $out/bin
-cd ${R}/bin
-for exe in *; do
-  makeWrapper ${R}/bin/$exe $out/bin/$exe \
-    --prefix "R_LIBS_SITE" ":" "$R_LIBS_SITE"
-done
-''