Invoke EVP_PKEY_set1_engine() if OpenSSL has it
Invoke EVP_PKEY_set1_engine() if OpenSSL has it

This approach was suggested by @mouse07410 in #185.

mtrojnar/libp11,dengert/libp11,dengert/libp11,mtrojnar/libp11,mouse07410/libp11,OpenSC/libp11,OpenSC/libp11,mouse07410/libp11