With LibreSSL 2.7.0 (or newer versions) some more structs have made
opaque, which requires a few changes:
- BIO_meth_new() and related functions are now defined by LibreSSL, the
versions from opensslcompat.{h,c} does not need to be used anymore.
- HMAC_CTX is now opaque, HMAC_CTX_new(), EVP_MD_CTX_new, and related
functions should be used instead in winpr's hash.c.