gnu: polkit: Fix elogind configuration.

* gnu/packages/patches/polkit-configure-elogind.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/polkit.scm (polkit): Use it.

gnu/local.mk

@@ -1599,6 +1599,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/plib-CVE-2011-4620.patch		\
   %D%/packages/patches/plib-CVE-2012-4552.patch		\
   %D%/packages/patches/plotutils-spline-test.patch		\
+  %D%/packages/patches/polkit-configure-elogind.patch		\
   %D%/packages/patches/polkit-use-duktape.patch			\
   %D%/packages/patches/portaudio-audacity-compat.patch		\
   %D%/packages/patches/portmidi-modular-build.patch		\

gnu/packages/patches/polkit-configure-elogind.patch

@@ -0,0 +1,15 @@
+Even when the polkit configure script detects elogind, it does not use
+it.  This patch ensures that elogind is used when it is detected.
+
+diff -ruN a/configure b/configure
+--- a/configure	1969-12-31 19:00:01.000000000 -0500
++++ b/configure	2021-11-19 00:04:55.581385020 -0500
+@@ -20390,7 +20390,7 @@
+ 
+ 
+ 
+- if test "$have_libsystemd" = "yes"; then
++ if test "$have_libsystemd" = "yes" || test "$have_libelogind" = "yes"; then
+   HAVE_LIBSYSTEMD_TRUE=
+   HAVE_LIBSYSTEMD_FALSE='#'
+ else

gnu/packages/polkit.scm

@@ -60,6 +60,7 @@
              (sha256
               (base32
                "00zfg9b9ivkcj2jcf5b92cpvvyljz8cmfwj86lkvy5rihnd5jypf"))
+             (patches (search-patches "polkit-configure-elogind.patch"))
              (modules '((guix build utils)))
              (snippet
               '(begin