gnu: nspr: Add $libdir to the RUNPATH of binaries.

* gnu/packages/gnuzilla.scm (nspr)[arguments]: Add
  LDFLAGS=-Wl,-rpath=$libdir to #:configure-flags.

gnu/packages/gnuzilla.scm

@@ -104,10 +104,11 @@ in C/C++.")
       `(("perl", perl)))
     (arguments
      `(#:tests? #f ; no check target
-        #:configure-flags
-        `("--enable-64bit")
-        #:phases
-          (alist-cons-before
+       #:configure-flags (list "--enable-64bit"
+                               (string-append "LDFLAGS=-Wl,-rpath="
+                                              (assoc-ref %outputs "out")
+                                              "/lib"))
+       #:phases (alist-cons-before
                  'configure 'chdir
                  (lambda _
                    (chdir "nspr"))