mkmf.rb: avoid interference
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49482 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
mkmf.rb: avoid interference
interference by modifying global variables in have_devel? method.
[ruby-core:67962] [Bug #10821]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49482 b2dd03c8-39d4-4d8f-98ff-823fe69b080e