openssl: Add a generic private key loader

src/libstrongswan/plugins/openssl/openssl_util.h

@@ -135,6 +135,13 @@ int openssl_asn1_known_oid(ASN1_OBJECT *obj);
  */
 time_t openssl_asn1_to_time(ASN1_TIME *time);
 
+/**
+ * Compatibility macros
+ */
+#ifdef OPENSSL_IS_BORINGSSL
+#define EVP_PKEY_base_id(p) EVP_PKEY_type(p->type)
+#endif
+
 /**
  * Macros to define fallback getters/setters to access keys (BIGNUM*) for types
  * that were made opaque with OpenSSL 1.1.0.