build: fix OpenSSL EC detection on macOS

[fanquake]

Fixes #734.

The first commit fixes OpenSSL EC detection on macOS, by making CRYPTO_CPPFLAGS available during configure. Similar to how GMP_CPPFLAGS are used.

The second commit, which I'd like feedback on, fixes a compilation error:

  CC       src/bench_verify.o
src/bench_verify.c:15:10: fatal error: 'openssl/bn.h' file not found
#include <openssl/bn.h>
         ^~~~~~~~~~~~~~
1 error generated.

as CRYPTO_CPPFLAGS are then needed in bench_verify, and are not included otherwise.

Not sure if this is the way you'd like to fix this, as its a bit of a hack for macOS.

[real-or-random]

Thanks! I'm fine with the code changes but I can't test on macOS. The second commit seems correct and I don't see why it should be a hack.

[gwillen]

I have a mac (10.14.6) and am willing to test this -- can someone give me a fairly precise description of a negative test and a positive test for me to try?

[fanquake]

@gwillen

Master 4f27e34:

./configure --enable-openssl-tests
...
checking for libcrypto... yes
checking for main in -lcrypto... yes
checking for EC functions in libcrypto... no
configure: error: OpenSSL tests requested but OpenSSL with EC support is not available

This PR @ 84b5fc5. Configure works, compiling doesn't:

./configure --enable-openssl-tests
# make files
  CC       src/bench_verify.o
src/bench_verify.c:15:10: fatal error: 'openssl/bn.h' file not found
#include <openssl/bn.h>
         ^~~~~~~~~~~~~~
1 error generated.

This PR @ 3b7d26b. Everything works as expected.

[gwillen]

Is this all meant to be done with brew's openssl linked? On my system, brew says:

openssl@1.1 is keg-only, which means it was not symlinked into /usr/local, because openssl/libressl is provided by macOS so don't link an incompatible version.

And I get the configure error regardless of which version I check out.

[fanquake]

Is this all meant to be done with brew's openssl linked?

No

I get the configure error regardless of which version I check out.

Did you run autogen.sh before running configure after checking out the changes?

[gwillen]

Aha, nope I did not. That causes the behavior to be exactly as predicted! Configure works at 84b5fc5, build works at 3b7d26b. Let me know if you want me to check anything else.

[real-or-random]

ACK 3b7d26b the diff looks good to me

I think it's okay to merge this before now even though #738 is there. If we think that we can quickly merge #738, we can also do this instead.

[jonasnick]

ACK 3b7d26b