* add no_arm64 tag to resolver_component_tests_runner_invoker tests
* skip no_arm64 tests when running on arm64
* increase kokoro jobs timeout for ARM64 C/C++ bazel tests
* use 8 core instance for arm64 bazel C/C++ tests
This replaces gflags. Added TODOs where use of `absl::Duration` or `absl::FlagSaver` might be preferred in follow-up cleanup. Fixes#24493.
This reverts commit da66b7d14e.
NEW:
* Adds references to `absl/flags/declare.h`, new to LTS 2020923.2 imported in commit 5b43440.
* Works around MSVC 2017 compiler error with large help text on flags by reducing the help text.
Bazel builds of test/cpp/end2end:end2end_test were failing on Mac OS with v1.8.0 due to missing gtest symbols. The issue is not seen in v1.8.1. A WORKSPACE file was added to gtest repo in 1.8.1, so gtest.BUILD can be removed.