BUILD: ssl: fine guard for SSL_CTX_get0_privatekey call

SSL_CTX_get0_privatekey is openssl/boringssl specific function present
since openssl-1.0.2, let us define readable guard for it, not depending
on HA_OPENSSL_VERSION

(cherry picked from commit af204881a3df36da1451af33f57b2c11ecb0972e)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
2 files changed