setup.sh: avoid running the same hook twice

In strictDeps=false, we don’t want the same package hook to be run
twice, otherwise we get duplicates in some flags.

Fixes #41340

pkgs/stdenv/generic/setup.sh

@@ -562,6 +562,10 @@ _addToEnv() {
             (( "$depHostOffset" <= "$depTargetOffset" )) || continue
             local hookRef="${hookVar}[$depTargetOffset - $depHostOffset]"
             if [[ -z "${strictDeps-}" ]]; then
+
+                # Keep track of which packages we have visited before.
+                local visitedPkgs=""
+
                 # Apply environment hooks to all packages during native
                 # compilation to ease the transition.
                 #
@@ -574,7 +578,11 @@ _addToEnv() {
                     ${pkgsHostTarget+"${pkgsHostTarget[@]}"} \
                     ${pkgsTargetTarget+"${pkgsTargetTarget[@]}"}
                 do
+                    if [[ "$visitedPkgs" = *"$pkg"* ]]; then
+                        continue
+                    fi
                     runHook "${!hookRef}" "$pkg"
+                    visitedPkgs+=" $pkg"
                 done
             else
                 local pkgsRef="${pkgsVar}[$depTargetOffset - $depHostOffset]"