Move RPATH shrinking from stdenv to a setup hook provided by patchelf

pkgs/development/tools/misc/patchelf/setup-hook.sh

@@ -0,0 +1,18 @@
+# This setup hook calls patchelf to automatically remove unneeded
+# directories from the RPATH of every library or executable in every
+# output.
+
+if [ -z "$dontPatchELF" ]; then
+    addHook fixupOutput 'patchELF "$prefix"'
+fi
+
+patchELF() {
+    header "patching ELF executables and libraries in $prefix"
+    if [ -e "$prefix" ]; then
+        find "$prefix" \( \
+            \( -type f -a -name "*.so*" \) -o \
+            \( -type f -a -perm +0100 \) \
+            \) -print -exec patchelf --shrink-rpath '{}' \;
+    fi
+    stopNest
+}