calculate correct stack depth at compile time.
* insns.def (emptstack): remove it and add a new insn "adjuststack".
* bootstraptest/test_knownbug.rb: move/remove fixed test.
* bootstraptest/test_syntax.rb: ditto.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@15245 b2dd03c8-39d4-4d8f-98ff-823fe69b080e