-DMYSQL_MAINTAINER_MODE=NO

also add =WARN as an alias for =OFF
and clarify the help text

CMakeLists.txt

@@ -134,7 +134,7 @@ IF(DEFINED ENV{CPPFLAGS})
   ADD_DEFINITIONS($ENV{CPPFLAGS})
 ENDIF()
 
-SET(MYSQL_MAINTAINER_MODE "AUTO" CACHE STRING "MySQL maintainer-specific development environment. Options are: ON OFF AUTO.")
+SET(MYSQL_MAINTAINER_MODE "AUTO" CACHE STRING "Enable MariaDB maintainer-specific warnings. One of: NO (warnings are disabled) WARN (warnings are enabled) ERR (warnings are errors) AUTO (warnings are errors in Debug only)")
 
 # Packaging
 IF (NOT CPACK_GENERATOR)

cmake/maintainer.cmake

 # Copyright (c) 2010, 2014, Oracle and/or its affiliates. All rights reserved.
-# Copyright (c) 2020, MariaDB
+# Copyright (c) 2011, 2021, MariaDB
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -14,6 +14,10 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA
 
+IF(MYSQL_MAINTAINER_MODE STREQUAL "NO")
+  RETURN()
+ENDIF()
+
 # Common warning flags for GCC, G++, Clang and Clang++
 SET(MY_WARNING_FLAGS
   -Wall
@@ -41,7 +45,7 @@ IF(CMAKE_COMPILER_IS_GNUCC AND CMAKE_C_COMPILER_VERSION VERSION_LESS "6.0.0")
   SET(MY_ERROR_FLAGS ${MY_ERROR_FLAGS} -Wno-error=maybe-uninitialized)
 ENDIF()
 
-IF(MYSQL_MAINTAINER_MODE MATCHES "OFF")
+IF(MYSQL_MAINTAINER_MODE MATCHES "OFF|WARN")
   RETURN()
 ELSEIF(MYSQL_MAINTAINER_MODE MATCHES "AUTO")
   SET(WHERE DEBUG)