Configure: variable expand GENERATE values too

Internal documentation doesn't allow for any exception...  Therefore,
even GENERATE values should be variable expanded.

(there are historical reasons why GENERATE was excepted from variable
expansion, that aren't applicable any more)

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/15554)

Configure

diff --git a/Configure b/Configure
index 3a9ef03..f6951bb 100755
--- a/Configure
+++ b/Configure
@@ -2212,7 +2212,7 @@
                          if !@skip || $skip[$#skip] > 0; },
             qr/^\s* GENERATE ${index_re} = ${value_re} $/x
             => sub { $push_to->(\%generate, $expand_variables->($+{INDEX}),
-                                undef, undef, $+{VALUE})
+                                undef, undef, $expand_variables->($+{VALUE}))
                          if !@skip || $skip[$#skip] > 0; },
             qr/^\s* (?:\#.*)? $/x => sub { },
             "OTHERWISE" => sub { die "Something wrong with this line:\n$_\nat $sourced/$f" },