Don't check for _sys_siglist if sys_siglist is found.

configure

@@ -27942,10 +27942,9 @@ fi
 printf "%s\n" "#define HAVE_DECL_SYS_SIGLIST $ac_have_decl" >>confdefs.h
 if test $ac_have_decl = 1
 then :
-
   HAVE_SIGLIST="true"
-
-fi
+else case e in #(
+  e)
 	ac_fn_check_decl "$LINENO" "_sys_siglist" "ac_cv_have_decl__sys_siglist" "
 $ac_includes_default
 #include <signal.h>
@@ -27961,9 +27960,11 @@ fi
 printf "%s\n" "#define HAVE_DECL__SYS_SIGLIST $ac_have_decl" >>confdefs.h
 if test $ac_have_decl = 1
 then :
-
   HAVE_SIGLIST="true"
+fi
 
+     ;;
+esac
 fi
 
     if test "$HAVE_SIGLIST" != "true"; then

configure.ac

@@ -3382,9 +3382,12 @@ AC_CHECK_FUNCS([strsignal], [], [
     AC_LIBOBJ(strsignal)
     SUDO_APPEND_COMPAT_EXP(sudo_strsignal)
     HAVE_SIGLIST="false"
-    AC_CHECK_DECLS([sys_siglist, _sys_siglist], [
-	HAVE_SIGLIST="true"
-    ], [ ], [
+    AC_CHECK_DECLS([sys_siglist], [HAVE_SIGLIST="true"], [
+	AC_CHECK_DECLS([_sys_siglist], [HAVE_SIGLIST="true"], [], [
+AC_INCLUDES_DEFAULT
+#include <signal.h>
+	])
+    ], [
 AC_INCLUDES_DEFAULT
 #include <signal.h>
     ])