merge revision(s) r45542,r45543: [Backport #9717]

	* gc.c (mark_current_machine_context): Call SET_STACK_END.
	  This reverts a hunk of r40703 by ko1.
	  This fixes [ruby-dev:48098] [Bug #9717].


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47229 b2dd03c8-39d4-4d8f-98ff-823fe69b080e