[SECP256K1] Make autotools check for all the used openssl functions
Summary:
I added all the openssl functions that we call in tests.c and in bench_verify.c to the m4 check, that way if any of them are missing it won't enable openssl. I also modified it a little to prevent a segmentation fault when running that program (not that it really matters for autotools)
Backport of secp256k1 PR838.
Test Plan:
make check
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Subscribers: deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D8157