cmake mruby: suppress a known warning
cmake mruby: suppress a known warning

kenhys/groonga,kenhys/groonga,kenhys/groonga,groonga/groonga,groonga/groonga,kenhys/groonga,groonga/groonga,groonga/groonga,groonga/groonga,kenhys/groonga,kenhys/groonga,kenhys/groonga,groonga/groonga,groonga/groonga,groonga/groonga,kenhys/groonga