merge revision(s) r45003: [Backport #9481]

	ext/psych/yaml: suppress warnings

	* ext/psych/yaml/emitter.c (WRITE_BREAK, PUT_BREAK): suppress
  unused-value warnings.

	* ext/psych/yaml/parser.c, ext/psych/yaml/scanner.c: suppress
  unused-but-set-variable warnings.

	* ext/psych/yaml/yaml_private.h (STACK_EMPTY): ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@45077 b2dd03c8-39d4-4d8f-98ff-823fe69b080e