crypto.ecdsa: add support for OpenSSL on OpenBSD

[lcheylus]

On OpenBSD, LibreSSL (https://www.libressl.org/) is used by default as TLS/crypto stack. This library is not fully compatible with OpenSSL v3.

OpenSSL v3.4 could be installed on OpenBSD via eopenssl34 package available in official ports tree.

This PR adds support for OpenSSL version 3.4 (more recent version available for 7.7 release) on OpenBSD :

• cmd/tools/modules/testing/common.v: add special case for OpenBSD to check if OpenSSL is present
• vlib/crypto/ecdsa/ecdsa.c.v: add flags for OpenSSL to find OpenSSL v3.4 includes/libs
• disable tests for OpenBSD with gcc in crypto/ecdsa: issues to find OpenSSL symbols during link (unable to fix theses errors for now).

---

Tests OK on OpenBSD/amd64 with tcc, clang and gcc for vlib/crypto, vlib/net/ssl/ and vlib/net/openssl/

$ ./v -cc tcc -W test vlib/crypto/
(...)
Summary for all V _test.v files: 64 passed, 64 total. Elapsed time: 31790 ms, on 3 parallel jobs. Comptime: 65572 ms. Runtime: 28527 ms.

$ ./v -cc tcc -W test vlib/net/ssl/
---- Testing... ----------------------------------------------------------------------------------------------------------------------------
 OK       9.164 ms vlib/net/ssl/ssl_compiles_test.v
--------------------------------------------------------------------------------------------------------------------------------------------
Summary for all V _test.v files: 1 passed, 1 total. Elapsed time: 1221 ms, on 1 job. Comptime: 1206 ms. Runtime: 9 ms.

$ ./v -cc tcc -W test vlib/net/openssl/
---- Testing... ----------------------------------------------------------------------------------------------------------------------------
 OK       8.713 ms vlib/net/openssl/openssl_compiles_test.c.v
--------------------------------------------------------------------------------------------------------------------------------------------
Summary for all V _test.v files: 1 passed, 1 total. Elapsed time: 948 ms, on 1 job. Comptime: 935 ms. Runtime: 8 ms.

[huly-for-github]

Connected to Huly®: V_0.6-23189

[spytheman]

Excellent work.