mruby/mruby — pull request #633 by xxuejie (2012-12-16 16:12:00+00:00)
Title: Define DISABLE_GEMS flag based on the value of ENABLE_GEMS in Makefile

Currently, to enable mrbgems, we have to change two values:

* set ```ENABLE_GEMS``` to ```true``` in *$(MRUBY_ROOT)/Makefile*
* comment out ```DISABLE_GEMS``` in *$(MRUBY_ROOT)/include/mrbconf.h*

And of course, we also need to modify the *GEMS.active* file.

This may bring some inconsistency: if we set ```ENABLE_GEMS``` to ```true``` but forgot to comment out ```DISABLE_GEMS```, we still cannot use mrbgems.

This commit add ```DISABLE_GEMS``` as a command line flag to the compiler, so we only need to set the value of ```ENABLE_GEMS``` here.