gnu: Add openssl-next.

* gnu/packages/tls.scm (openssl-next): New variable.
* gnu/packages/patches/openssl-1.1.0-c-rehash-in.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu/packages/patches/openssl-1.1.0-c-rehash-in.patch

@@ -0,0 +1,19 @@
+This patch removes the explicit reference to the 'perl' binary,
+such that OpenSSL does not retain a reference to Perl.
+
+The 'c_rehash' program is seldom used, but it is used nonetheless
+to create symbolic links to certificates, for instance in the 'nss-certs'
+package.
+
+diff --git a/tools/c_rehash.in b/tools/c_rehash.in
+index 2fef627..9d40eae 100644
+--- a/tools/c_rehash.in
++++ b/tools/c_rehash.in
+@@ -1,4 +1,6 @@
+-#!{- $config{hashbangperl} -}
++eval '(exit $?0)' && eval 'exec perl -wS "$0" ${1+"$@"}'
++  & eval 'exec perl -wS "$0" $argv:q'
++    if 0;
+ 
+ # {- join("\n# ", @autowarntext) -}
+ # Copyright 1999-2016 The OpenSSL Project Authors. All Rights Reserved.