configdata.pm.in: Don't try to quotify undefined values

Fixes #10503

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/10548)

configdata.pm.in

diff --git a/configdata.pm.in b/configdata.pm.in
index 3121226..71627b4 100644
--- a/configdata.pm.in
+++ b/configdata.pm.in
@@ -245,7 +245,13 @@
         foreach (sort keys %target) {
             next if $_ =~ m|^_| || $_ eq 'template';
             my $quotify = sub {
-                map { (my $x = $_) =~ s|([\\\$\@"])|\\$1|g; "\"$x\""} @_;
+                map {
+                    if (defined $_) {
+                        (my $x = $_) =~ s|([\\\$\@"])|\\$1|g; "\"$x\""
+                    } else {
+                        "undef";
+                    }
+                } @_;
             };
             print '    ', $_, ' => ';
             if (ref($target{$_}) eq "ARRAY") {