Undo static linking and other workarounds that are no longer needed
after the bump

Rework dhtest to use accessors and link statically for now

Include -DLIBRESSL_INTERNAL in regress makefiles.

ok miod@

Build these tests with WARNINGS=Yes and -Werror, and do the necessary
fixes to keep building.

Import the OpenSSL libcrypto tests in a form suitable for our rergress
infrastructure.
The following tests have not been imported, for their code lacks a licence:
asn1, rsa, sha256, sha512, wp.