http: use new API with LibreSSL >=2.7.0
LibreSSL is not yet fully API compatible with OpenSSL 1.0.2 and later, However many APIs from OpenSSL and 1.0.2 and 1.1 are already implemented in LibreSSL 2.7.0 and later. Old approach works in newer LibreSSL version as well, but it's not nice to force deprecated functions on LibreSSL users.
Add additional conditionals for new LibreSSL versions to use the available new APIs.