Clean up aarch64 tests.

This bumps us to gcc 6 (rather than 4.8), which fully supports C++14, and migrates the Python tests to our Bazel-based system.  C#, PHP, and Ruby will remain on CMake + alternate build system for now.

PiperOrigin-RevId: 495501807
diff --git a/python/BUILD.bazel b/python/BUILD.bazel
index d40e76a..cc0772c 100644
--- a/python/BUILD.bazel
+++ b/python/BUILD.bazel
@@ -10,6 +10,7 @@
 load("@rules_python//python:defs.bzl", "py_library")
 load("@pip_deps//:requirements.bzl", "requirement")
 load("//:protobuf.bzl", "internal_py_proto_library")
+load("//build_defs:arch_tests.bzl", "aarch64_test", "x86_64_test")
 load("//build_defs:cpp_opts.bzl", "COPTS")
 load("//conformance:defs.bzl", "conformance_test")
 load(":internal.bzl", "internal_copy_files", "internal_py_test")
@@ -118,6 +119,22 @@
     }),
 )
 
+aarch64_test(
+    name = "aarch64_test",
+    bazel_binaries = [
+        "google/protobuf/internal/_api_implementation.so",
+        "google/protobuf/pyext/_message.so",
+    ],
+)
+
+x86_64_test(
+    name = "x86_64_test",
+    bazel_binaries = [
+        "google/protobuf/internal/_api_implementation.so",
+        "google/protobuf/pyext/_message.so",
+    ],
+)
+
 py_library(
     name = "python_srcs",
     srcs = glob(