OpenSSL 1.1 made some CTX structures opaque. Port our code to use the
structures only through pointers via OpenSSL 1.1 APIs. Use our adaption
layer to make this work with OpenSSL 1.0 and below.
Patch-by: Tomas Mraz <tmraz@redhat.com>
Patch-from: https://bugzilla.redhat.com/1383744
Add private forwarding headers for `openssl/{evp,hmac}.h` to give us a
central place to add adaptation code to work across multiple
incompatible OpenSSL versions. Provide compatibility implementations of
some OpenSSL 1.1 APIs when using older OpenSSL versions.
Brad King