driver.rb: add option to specify target with rbenv

[close GH-1724]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60299 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

benchmark/driver.rb

@@ -381,6 +381,11 @@ if __FILE__ == $0
          opt[:execs] << path
        }
     }
+    o.on('--rbenv [VERSIONS]', 'Specify benchmark targets with rbenv version (vX.X.X;vX.X.X;...)'){|v|
+      v.split(/;/).each{|version|
+        opt[:execs] << "#{version}::#{`RBENV_VERSION='#{version}' rbenv which ruby`.rstrip}"
+      }
+    }
     o.on('-d', '--directory [DIRECTORY]', "Benchmark suites directory"){|d|
       opt[:dir] = d
     }