* gc.c: We have no chance to expand the heap when lazy sweeping is
  restricted. So collecting is often invoked if there is not
  enough free space in the heap. Try to expand heap when this is
  the case.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39900 b2dd03c8-39d4-4d8f-98ff-823fe69b080e