test_optimization.rb: tailcall

	* test/ruby/test_optimization.rb (TestRubyOptimization.tailcall):
  helper method to compile methods with tailcall optimization
  enabled.
	* compile.c (iseq_optimize): disable tail call optimization in
	  rescued, rescue, and ensure blocks.
	  [ruby-core:73871] [Bug #12082]

	* compile.c (new_label_body): initialize bit fields, since
	  compile_data_alloc does not clear the memory.  [Bug #12082]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@54715 b2dd03c8-39d4-4d8f-98ff-823fe69b080e