merge revision(s) f1b76ea6,1d1f98d4: [Backport #16024]

	Occupy match data

	* string.c (rb_str_split_m): occupy match data not to be modified
	  during yielding the block.  [Bug #16024]

	Reuse match data

	* string.c (rb_str_split_m): reuse occupied match data.  [Bug #16024]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@67743 b2dd03c8-39d4-4d8f-98ff-823fe69b080e