gnu: iptables: Fix cross-compilation.

* gnu/packages/linux.scm (iptables)[arguments]:
Rewrite as G-expression to avoid %OUTPUT when cross-compiling.

gnu/packages/linux.scm

@@ -2642,9 +2642,13 @@ external rate conversion.")
     (inputs
      (list libmnl libnftnl/fixed))
     (arguments
-     '(#:tests? #f       ; no test suite
-       #:configure-flags ; add $libdir to the RUNPATH of executables
-       (list (string-append "LDFLAGS=-Wl,-rpath=" %output "/lib"))))
+     (list #:tests? #f             ; no test suite
+           #:configure-flags       ; add $libdir to the RUNPATH of executables
+           ;; XXX TODO: Replace with simply #$OUTPUT on core-updates.
+           #~(list (string-append "LDFLAGS=-Wl,-rpath="
+                                  #$(if (%current-target-system)
+                                        #~#$output
+                                        #~%output) "/lib"))))
     (home-page "https://www.netfilter.org/projects/iptables/index.html")
     (synopsis "Programs to configure Linux IP packet filtering rules")
     (description