MDEV-16478: mysql_real_connect() from libmariadbd.so always crash

Returned accidentally removed undefinition of MYSQL_SERVER in net_serv.cc inside embedded server
(embedded server uses real_net_read/write only as a client)

Prevented attempt to clean up embedded server if it was not initialized

unittest/embedded/CMakeLists.txt

@@ -0,0 +1,20 @@
+
+INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR}/include
+                    ${CMAKE_SOURCE_DIR}/libmysqld/include
+                    ${PCRE_INCLUDES}
+                    ${CMAKE_SOURCE_DIR}/sql
+                    ${MY_READLINE_INCLUDE_DIR}
+                    )
+
+
+ADD_DEFINITIONS(-DEMBEDDED_LIBRARY -UMYSQL_CLIENT)
+
+
+MYSQL_ADD_EXECUTABLE(test-connect-t test-connect.cc
+               COMPONENT Test)
+TARGET_LINK_LIBRARIES(test-connect-t mysqlserver )
+MY_ADD_TEST(test-connect)
+
+IF(UNIX)
+SET_TARGET_PROPERTIES(test-connect-t PROPERTIES ENABLE_EXPORTS TRUE)
+ENDIF()

unittest/embedded/test-connect.cc

@@ -0,0 +1,78 @@
+#include <mysql.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int get_evar(char **hostname, char **port, char** username, char ** password)
+{
+
+  if (!((*hostname)= getenv("MYSQL_TEST_HOST")))
+    (*hostname)= (char *)"127.0.0.1";
+
+  if (!((*port)= getenv("MASTER_MYPORT")))
+  {
+    if (!((*port)= getenv("MYSQL_TEST_PORT")))
+      return 1;
+  }
+
+  if (!((*username)= getenv("MYSQL_TEST_USER")))
+    (*username)= (char *)"root";
+
+  if (!((*password)= getenv("MYSQL_TEST_PASSWD")))
+    (*password)= (char *)"";
+
+  return 0;
+}
+
+int main(int argc, char *argv[])
+{
+  MYSQL *mysql;
+  char *host;
+  char *user;
+  char *passwd;
+  char *porta;
+  unsigned int port;
+
+  if (get_evar(&host, &porta, &user, &passwd))
+  {
+    printf("set environment variable MASTER_MYPORT\n");
+    return 1;
+  }
+
+  port = atoi(porta);
+
+  mysql_thread_init();
+
+  if (mysql_server_init(-1, NULL, NULL) != 0) {
+    printf("mysql_library_init failed");
+    return 1;
+  }
+
+
+  mysql = mysql_init(NULL);
+
+  if (!mysql) {
+    printf("mysql_init failed");
+    return 1;
+  }
+
+  if (mysql_options(mysql, MYSQL_OPT_USE_REMOTE_CONNECTION, NULL) != 0) {
+    printf("mysql_options MYSQL_OPT_USE_REMOTE_CONNECTION failed: %s\n", mysql_error(mysql));
+    return 1;
+  }
+
+  if (mysql_options(mysql, MYSQL_SET_CHARSET_NAME, "utf8mb4") != 0) {
+    printf("mysql_options MYSQL_SET_CHARSET_NAME utf8mb4 failed: %s\n", mysql_error(mysql));
+    return 1;
+  }
+
+  if (!mysql_real_connect(mysql, host, user, passwd, NULL, port, NULL, CLIENT_FOUND_ROWS | CLIENT_MULTI_RESULTS | CLIENT_REMEMBER_OPTIONS)) {
+    printf("mysql_real_connect failed: %s\n", mysql_error(mysql));
+    return 1;
+  }
+  mysql_close(mysql);
+  mysql_thread_end();
+  mysql_library_end();
+
+  return 0;
+
+}