fix signature decoding for overdubbed functions

src/compiler/irgen.jl

@@ -25,7 +25,7 @@ function backtrace(job::CompilerJob, call_stack::Vector{Core.MethodInstance})
  # calls to overdub directly, the backtrace therefore is collapsed and we have to
  # lookup the overdubbed function, but only if we likely are using the generated variant.
  actual_sig = Tuple{method_instance.specTypes.parameters[3:end]...}
- m = ccall(:jl_gf_invoke_lookup, Any, (Any, UInt), tt, typemax(UInt))
+ m = ccall(:jl_gf_invoke_lookup, Any, (Any, UInt), actual_sig, typemax(UInt))
  method = m.func::Method
  end
  frame = StackTraces.StackFrame(method.name, method.file, method.line)