Configure: Improve warning if no random seed source was configured

The new Configure summary box (41349b5) now hides the warning
about the missing seed source (2805ee1) too much. To make it
more visible again, add warning markers.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from #7509)

Configure

@@ -1013,13 +1013,18 @@ if (scalar(@seed_sources) == 0) {
 if (scalar(grep { $_ eq 'none' } @seed_sources) > 0) {
     die "Cannot seed with none and anything else" if scalar(@seed_sources) > 1;
     warn <<_____ if scalar(@seed_sources) == 1;
-You have selected the --with-rand-seed=none option, which effectively disables
-automatic reseeding of the OpenSSL random generator. All operations depending
-on the random generator such as creating keys will not work unless the random
-generator is seeded manually by the application.
 
-Please read the 'Note on random number generation' section in the INSTALL
-instructions and the RAND_DRBG(7) manual page for more details.
+============================== WARNING ===============================
+You have selected the --with-rand-seed=none option, which effectively
+disables automatic reseeding of the OpenSSL random generator.
+All operations depending on the random generator such as creating keys
+will not work unless the random generator is seeded manually by the
+application.
+
+Please read the 'Note on random number generation' section in the
+INSTALL instructions and the RAND_DRBG(7) manual page for more details.
+============================== WARNING ===============================
+
 _____
 }
 push @{$config{openssl_other_defines}},