message: Update string representations for calling conventions
diff: @@ -2642,9 +2642,9 @@ const std::string FunctionType::GetNameForCallConv() const {
  case llvm::CallingConv::C:
  return "";
  case llvm::CallingConv::X86_VectorCall:
  - return "vectorcall";
  + return "__vectorcall";
  case llvm::CallingConv::X86_RegCall:
  - return "regcall";
  + return "__regcall";
  case llvm::CallingConv::SPIR_FUNC:
  return "spir_func";
  case llvm::CallingConv::SPIR_KERNEL:
  