make statement_costs! accept IRCode (JuliaLang#41257)

I want to use this in Cthulhu, which uses `IRCode` for optimized code
instead of `CodeInfo`.

base/compiler/optimize.jl

@@ -565,12 +565,14 @@ function inline_worthy(ir::IRCode,
  return true
 end
 
-function statement_costs!(cost::Vector{Int}, body::Vector{Any}, src::CodeInfo, sptypes::Vector{Any}, unionpenalties::Bool, params::OptimizationParams)
+function statement_costs!(cost::Vector{Int}, body::Vector{Any}, src::Union{CodeInfo, IRCode}, sptypes::Vector{Any}, unionpenalties::Bool, params::OptimizationParams)
  throw_blocks = params.unoptimize_throw_blocks ? find_throw_blocks(body) : nothing
  maxcost = 0
  for line = 1:length(body)
  stmt = body[line]
- thiscost = statement_or_branch_cost(stmt, line, src, sptypes, src.slottypes, unionpenalties, params, throw_blocks)
+ thiscost = statement_or_branch_cost(stmt, line, src, sptypes,
+ src isa CodeInfo ? src.slottypes : src.argtypes,
+ unionpenalties, params, throw_blocks)
  cost[line] = thiscost
  if thiscost > maxcost
  maxcost = thiscost