* configure.ac: removed DISABLE_RUBYGEMS macro from config.h, not
to rebuild everything when the flag changed.
* configure.ac, win32/configure.bat: make USE_RUBYGEMS lowercase.
* tool/mkconfig.rb: remove RUBYGEMS stuff from rbconfig.rb, not to
reconfigure and rebuild all extension libraries.
* Makefile.in (CPPFLAGS): enable/disable Rubygems by USE_RUBYGEMS.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63718 b2dd03c8-39d4-4d8f-98ff-823fe69b080e