Detect if EVP_MD_CTX_new is supported by OpenSSL

Summary: This is required to build bitcoin-qt

Test Plan:

cmake -GNinja ..

Make sure that the generated bitcoin-config.h contains the right infos.

Reviewers: schancel, #bitcoin_abc

Reviewed By: schancel, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D834