configure.in: add --with-jemalloc option

* configure.in: add --with-jemalloc option
  [ruby-core:62912]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46349 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-06-05

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46350 b2dd03c8-39d4-4d8f-98ff-823fe69b080e