configure.in: fix jemalloc option

* configure.in (jemalloc): fix option argument, should use
  `$withval` but not `yes` always.  [ruby-core:66994] [Bug #10625]
* configure.in (jemalloc): defer adding the liner option to get
  rid of linking contest against jemalloc, so that it works
  without runtime dynamic load path.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48907 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-12-21

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48908 b2dd03c8-39d4-4d8f-98ff-823fe69b080e