a patch for OpenVPN 2.4.5 to prevent errors when compiling with LibreSSL 2.6.4

openvpn-001-libressl_fix.patch

diff --git a/configure.ac b/configure.ac
index 88d1e09..7db5c79 100644
--- a/configure.ac
+++ b/configure.ac
@@ -935,6 +935,18 @@ if test "${enable_crypto}" = "yes" -a "${with_crypto_library}" = "openssl"; then
 			EC_GROUP_order_bits
 		]
 	)
+	AC_CHECK_DECL(
+		[
+			SSL_CTX_get_min_proto_version,
+			SSL_CTX_get_max_proto_version,
+			SSL_CTX_set_min_proto_version,
+			SSL_CTX_set_max_proto_version,
+		],
+		,
+		,
+		[[#include <openssl/ssl.h>]]
+
+	)
 
 	CFLAGS="${saved_CFLAGS}"
 	LIBS="${saved_LIBS}"
diff --git a/src/openvpn/openssl_compat.h b/src/openvpn/openssl_compat.h
index d375fab..340d452 100644
--- a/src/openvpn/openssl_compat.h
+++ b/src/openvpn/openssl_compat.h
@@ -661,7 +661,7 @@ EC_GROUP_order_bits(const EC_GROUP *group)
 #define RSA_F_RSA_OSSL_PRIVATE_ENCRYPT       RSA_F_RSA_EAY_PRIVATE_ENCRYPT
 #endif
 
-#ifndef SSL_CTX_get_min_proto_version
+#if !HAVE_DECL_SSL_CTX_GET_MIN_PROTO_VERSION
 /** Return the min SSL protocol version currently enabled in the context.
  *  If no valid version >= TLS1.0 is found, return 0. */
 static inline int
@@ -684,7 +684,7 @@ SSL_CTX_get_min_proto_version(SSL_CTX *ctx)
 }
 #endif /* SSL_CTX_get_min_proto_version */
 
-#ifndef SSL_CTX_get_max_proto_version
+#if !HAVE_DECL_SSL_CTX_GET_MAX_PROTO_VERSION
 /** Return the max SSL protocol version currently enabled in the context.
  *  If no valid version >= TLS1.0 is found, return 0. */
 static inline int
@@ -707,7 +707,7 @@ SSL_CTX_get_max_proto_version(SSL_CTX *ctx)
 }
 #endif /* SSL_CTX_get_max_proto_version */
 
-#ifndef SSL_CTX_set_min_proto_version
+#if !HAVE_DECL_SSL_CTX_SET_MIN_PROTO_VERSION
 /** Mimics SSL_CTX_set_min_proto_version for OpenSSL < 1.1 */
 static inline int
 SSL_CTX_set_min_proto_version(SSL_CTX *ctx, long tls_ver_min)
@@ -736,7 +736,7 @@ SSL_CTX_set_min_proto_version(SSL_CTX *ctx, long tls_ver_min)
 }
 #endif /* SSL_CTX_set_min_proto_version */
 
-#ifndef SSL_CTX_set_max_proto_version
+#if !HAVE_DECL_SSL_CTX_SET_MAX_PROTO_VERSION
 /** Mimics SSL_CTX_set_max_proto_version for OpenSSL < 1.1 */
 static inline int
 SSL_CTX_set_max_proto_version(SSL_CTX *ctx, long tls_ver_max)

Source here, I altered it to work with OpenVPN 2.4.5

Only works when autoconf is actually called (so it doesn't work for openvpn-build)