Ruby

fix redefinition optimization for -"literal string" (UMinus)

Unfortunately this enlarges insns.def by yet another
instruction. However, it is much prettier than opt_str_freeze
in use, and maybe we can avoid having so many instructions in
the future.

[ruby-core:80368]

• insns.def (DEFINE_INSN): new instruction: opt_str_uminus (maybe temporary)
• compile.c (iseq_compile_each0): split instructions
• test/ruby/test_optimization.rb (test_string_uminus): new test
• vm.c (vm_init_redefined_flag): set redefinintion flag for uminus
• vm_core.h (enum ruby_basic_operators): add BOP_UMINUS

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58144 b2dd03c8-39d4-4d8f-98ff-823fe69b080e