hare: add setupHook to configure HAREPATH

Add a setupHook so the HAREPATH environment variable is correctly set to
point to the hare stdlib and any third-party libraries.

pkgs/development/compilers/hare/hare.nix

@@ -37,6 +37,7 @@ stdenv.mkDerivation rec {
     qbe
   ];
 
+  setupHook = ./setup-hook.sh;
   strictDeps = true;
 
   configurePhase =

pkgs/development/compilers/hare/setup-hook.sh

@@ -0,0 +1,9 @@
+addHarepath () {
+    for haredir in third-party stdlib; do
+        if [[ -d "$1/src/hare/$haredir" ]]; then
+            addToSearchPath HAREPATH "$1/src/hare/$haredir"
+        fi
+    done
+}
+
+addEnvHooks "$hostOffset" addHarepath