setup.sh: Only load XDG_DATA_DIRS for executable inputs

This avoids the scenario where strictDeps is off and cross-compiled
XDG_DATA_DIRS content is brought into the environment.

While probably harmless for data like manpages and completion scripts,
this would cause issues when XDG_DATA_DIRS is used to find executables
or plugins. The Qt framework is known to behave like this and might
have run into incompatibilities.

pkgs/stdenv/generic/setup.sh

@@ -485,6 +485,9 @@ activatePackage() {
     # TODO(@Ericson2314): Don't special-case native compilation
     if [[ -z "${strictDeps-}" || "$hostOffset" -le -1 ]]; then
         addToSearchPath _PATH "$pkg/bin"
+    fi
+
+    if [[ "$hostOffset" -le -1 ]]; then
         addToSearchPath _XDG_DATA_DIRS "$pkg/share"
     fi