The missing #include <gshadow.h> causes the configure check to fail
spuriously, resulting in HAVE_SHADOWGRP not being defined.

Submitted upstream: <https://github.com/shadow-maint/shadow/pull/595>

diff --git a/configure.ac b/configure.ac
index 924254a0c8171802..6c7d9839979e037d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -116,6 +116,10 @@ if test "$ac_cv_header_shadow_h" = "yes"; then
 		ac_cv_libc_shadowgrp,
 		AC_RUN_IFELSE([AC_LANG_SOURCE([
 				#include <shadow.h>
+				#ifdef HAVE_GSHADOW_H
+				#include <gshadow.h>
+				#endif
+				int
 				main()
 				{
 					struct sgrp *sg = sgetsgent("test:x::");