Specify MRB_NO_BOXING to prevent panic on esp32.

Author: yuuu

components/mruby/build_config.rb

@@ -40,6 +40,8 @@
     cc.defines << %w(MRB_STR_BUF_MIN_SIZE=20)
     cc.defines << %w(MRB_GC_STRESS)
     cc.defines << %w(POOL_PAGE_SIZE=256)
+    cc.defines << %w(MRB_NO_BOXING)
+    cc.defines << %w(MRB_USE_METHOD_T_STRUCT)
   end
 
   conf.cxx do |cxx|

main/component.mk

@@ -1 +1,2 @@
 COMPONENT_DEPENDS = mruby
+CFLAGS += -DMRB_NO_BOXING