Fix safestack issues in ssl.h

Fix safestack issues in ssl.h

We fix 3 problems with safestack:
- Including an openssl header file without linking against libcrypto
  can cause compilation failures (even if the app does not otherwise need
  to link against libcrypto). See issue #8102
- Recent changes means that applications in no-deprecated builds will need
  to include additional macro calls in the source code for all stacks that
  they need to use - which is an API break. This changes avoids that
  necessity.
- It is not possible to write code using stacks that works in both a
  no-deprecated and a normal build of OpenSSL. See issue #12707.

Fixes #12707
Contains a partial fix for #8102. A similar PR will be needed for hash to
fully fix.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/12781)