Fix build errors with OpenSSL 3.0.x, but not deprecation warnings

This patch fixes errors only, so that build succeeds, but deprecation
warnings remain. It seems we need considerable changes to replace those
deprecated functions in the warnings.

Mk/main.mk

@@ -378,7 +378,11 @@ endif
 
 ifdef OPENSSL_FOUND
 PKG_CPPFLAGS+=	-I$(OPENSSL_FOUND)/include
+ifneq ($(findstring openssl-3.,$(OPENSSL_FOUND)),openssl-3.)
 PKG_LDFLAGS+=	-L$(OPENSSL_FOUND)/lib
+else
+PKG_LDFLAGS+=	-L$(OPENSSL_FOUND)/lib64
+endif
 PKG_LIBS+=	-lssl -lcrypto -lz
 endif
 ifdef LIBEVENT_FOUND

src/protossl.c

@@ -44,6 +44,11 @@
 static unsigned long ssl_session_context = 0x31415926;
 #endif /* USE_SSL_SESSION_ID_CONTEXT */
 
+#if OPENSSL_VERSION_NUMBER >= 0x30000000L
+#define ERR_GET_FUNC(x) 0
+#define ERR_func_error_string(x) ""
+#endif
+
 void
 protossl_log_ssl_error(struct bufferevent *bev, pxy_conn_ctx_t *ctx)
 {