gprbuild: fix rpath only when targeting darwin

pkgs/development/tools/build-managers/gprbuild/boot.nix

@@ -53,7 +53,14 @@ stdenv.mkDerivation {
   # introducing a wrapper for it in the future remains TODO.
   # For the moment this doesn't matter since we have no situation
   # were gprbuild is used to build something used at build time.
-  setupHook = ./gpr-project-path-hook.sh;
+  setupHooks = [
+    ./gpr-project-path-hook.sh
+  ] ++ lib.optionals stdenv.targetPlatform.isDarwin [
+    # This setupHook replaces the paths of shared libraries starting
+    # with @rpath with the absolute paths on Darwin, so that the
+    # binaries can be run without additional setup.
+    ./gpr-project-darwin-rpath-hook.sh
+  ];
 
   installPhase = ''
     runHook preInstall

pkgs/development/tools/build-managers/gprbuild/default.nix

@@ -17,7 +17,7 @@ stdenv.mkDerivation {
   inherit (gprbuild-boot)
     version
     src
-    setupHook
+    setupHooks
     meta
     ;
 

pkgs/development/tools/build-managers/gprbuild/gpr-project-darwin-rpath-hook.sh

@@ -0,0 +1,10 @@
+fixGprProjectDarwinRpath() {
+    for f in $(find $out -type f -executable); do
+        install_name_tool -id $f $f || true
+        for rpath in $(otool -L $f | grep @rpath | awk '{print $1}'); do
+            install_name_tool -change $rpath ${!outputLib}/lib/$(basename $rpath) $f || true
+        done
+    done
+}
+
+preFixupPhases+=" fixGprProjectDarwinRpath"

pkgs/development/tools/build-managers/gprbuild/gpr-project-path-hook.sh

@@ -6,16 +6,3 @@ addAdaObjectsPath() {
 }
 
 addEnvHooks "$targetOffset" addAdaObjectsPath
-
-fixDarwinRpath() {
-    for f in $(find $out -type f -executable); do
-        install_name_tool -id $f $f || true
-        for rpath in $(otool -L $f | grep rpath | awk '{print $1}'); do
-            install_name_tool -change $rpath $out/lib/$(basename $rpath) $f || true
-        done
-    done
-}
-
-if [ "$(uname)" = "Darwin" ]; then
-    preFixupPhases+=" fixDarwinRpath"
-fi