message: [SwiftLanguageRuntime] Fix the error return register on AArch64.
  No test as this fixes TestExpressionErrorBreakpoint there.
diff: @@ -3881,7 +3881,7 @@ llvm::Optional<Value> SwiftLanguageRuntime::GetErrorReturnLocationAfterReturn(
  error_reg_name = "r6";
  break;
  case llvm::Triple::ArchType::aarch64:
  - error_reg_name = "x19";
  + error_reg_name = "x21";
  break;
  case llvm::Triple::ArchType::x86_64:
  error_reg_name = "r12";
  @@ -3918,11 +3918,6 @@ llvm::Optional<Value> SwiftLanguageRuntime::GetErrorReturnLocationAfterReturn(
  const_cast<RegisterInfo *>(reg_info));
  error_val = val;
  }
  -// if (log)
  -// log->Printf("Found return address: 0x%" PRIu64 " from register %s.",
  -// return_addr,
  -// error_reg_name.str().c_str());
  -
  return error_val;
  }
  