merge revision(s) r45224,r45228: [Backport #9838]

	* gc.c (ruby_gc_set_params): fix building without RGenGC

	* gc.c (ruby_gc_set_params): simplify condition


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@46407 b2dd03c8-39d4-4d8f-98ff-823fe69b080e