signal.c: revert part of r46100

* signal.c (check_stack_overflow): revert part of r46100, the
  previous condition was correct, and fix compilation error on
  other architecture linux.  [ruby-core:62746] [Bug #9862]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46113 b2dd03c8-39d4-4d8f-98ff-823fe69b080e