Avoid using dataclass to support Python 3.6 on bionic

Author: kateinoigakukun

tools/build/build_support/platform.py

@@ -1,13 +1,12 @@
 import os
-from dataclasses import dataclass
 from typing import Optional
 
-@dataclass
 class PlatformInfo:
-    name: str
-    full_name: str
-    package_extension: str
-    arch: str
+    def __init__(self, name: str, full_name: str, package_extension: str, arch: str):
+        self.name = name
+        self.full_name = full_name
+        self.package_extension = package_extension
+        self.arch = arch
 
     def derive():
         uname = os.uname()

tools/build/package-toolchain

@@ -3,19 +3,18 @@
 import sys
 import os
 import argparse
-from dataclasses import dataclass
 from build_support.actions import Action, ActionRunner, DownloadBaseSnapshotAction, derive_options_from_args
 from build_support.platform import PlatformInfo
 
 
-@dataclass
 class SnapshotInfo:
-    year: int
-    month: int
-    day: int
-    toolchain_name: str
-    tarball_name: str
-    daily_snapshot: bool
+    def __init__(self, year: int, month: int, day: int, toolchain_name: str, tarball_name: str, daily_snapshot: bool):
+        self.year = year
+        self.month = month
+        self.day = day
+        self.toolchain_name = toolchain_name
+        self.tarball_name = tarball_name
+        self.daily_snapshot = daily_snapshot
 
 
 class PackageAction(Action):