fix compile of test/test_ecdsa_deterministic on OS X

[mringwal]

The test uses SHA256 from openssl. This changes adds -lcryto to the ldflags

Error without the fix:
Undefined symbols for architecture x86_64:
"_SHA256_Final", referenced from:
_finish_SHA256 in test_ecdsa_deterministic.o
"_SHA256_Init", referenced from:
_init_SHA256 in test_ecdsa_deterministic.o
"_SHA256_Update", referenced from:
_update_SHA256 in test_ecdsa_deterministic.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

[kmackay]

Hmm, I haven't looked at 'static' branch in a long time. I'd prefer to just rename the test to "test_ecdsa_deterministic.c.example" (like I did in master branch) rather than require linking against OpenSSL.