Releasing hermetic_cc_toolchain v2.0.0

Output of `zig build-exe` depends on the CPU, making it
non-reproducible. With `-mcpu` it's fine.

Similar to #22

The current release contains 3 redundant directories:

    $ tar -tf hermetic_cc_toolchain-v2.0.0.tar.gz | grep tools
    tools/
    tools/releaser/
    tools/releaser/data/

This change gets rid of them:

    $ tar -tvf hermetic_cc_toolchain-v99.0.0.tar.gz
    -rw-rw-r-- 0/0            1120 2000-01-01 02:00 LICENSE
    -rw-rw-r-- 0/0             561 2000-01-01 02:00 MODULE.bazel
    drwxrwxr-x 0/0               0 2000-01-01 02:00 toolchain/
    -rw-rw-r-- 0/0               0 2000-01-01 02:00 toolchain/BUILD
    -rw-rw-r-- 0/0             407 2000-01-01 02:00 toolchain/BUILD.sdk.bazel
    -rw-rw-r-- 0/0           11180 2000-01-01 02:00 toolchain/defs.bzl
    drwxrwxr-x 0/0               0 2000-01-01 02:00 toolchain/libc/
    -rw-rw-r-- 0/0             405 2000-01-01 02:00 toolchain/libc/BUILD
    -rw-rw-r-- 0/0             300 2000-01-01 02:00 toolchain/libc/defs.bzl
    drwxrwxr-x 0/0               0 2000-01-01 02:00 toolchain/libc_aware/
    drwxrwxr-x 0/0               0 2000-01-01 02:00 toolchain/libc_aware/platform/
    -rw-rw-r-- 0/0             261 2000-01-01 02:00 toolchain/libc_aware/platform/BUILD
    drwxrwxr-x 0/0               0 2000-01-01 02:00 toolchain/libc_aware/toolchain/
    -rw-rw-r-- 0/0             264 2000-01-01 02:00 toolchain/libc_aware/toolchain/BUILD
    drwxrwxr-x 0/0               0 2000-01-01 02:00 toolchain/platform/
    -rw-rw-r-- 0/0             164 2000-01-01 02:00 toolchain/platform/BUILD
    -rw-rw-r-- 0/0            1493 2000-01-01 02:00 toolchain/platform/defs.bzl
    drwxrwxr-x 0/0               0 2000-01-01 02:00 toolchain/private/
    -rw-rw-r-- 0/0               0 2000-01-01 02:00 toolchain/private/BUILD
    -rw-rw-r-- 0/0            2935 2000-01-01 02:00 toolchain/private/cc_toolchains.bzl
    -rw-rw-r-- 0/0            7599 2000-01-01 02:00 toolchain/private/defs.bzl
    drwxrwxr-x 0/0               0 2000-01-01 02:00 toolchain/toolchain/
    -rw-rw-r-- 0/0             167 2000-01-01 02:00 toolchain/toolchain/BUILD
    -rw-rw-r-- 0/0            2049 2000-01-01 02:00 toolchain/toolchain/defs.bzl
    -rw-rw-r-- 0/0           14372 2000-01-01 02:00 toolchain/zig-wrapper.zig
    -rw-rw-r-- 0/0            6010 2000-01-01 02:00 toolchain/zig_toolchain.bzl
    -rw-rw-r-- 0/0             358 2000-01-01 02:00 README
    -rw-rw-r-- 0/0              42 2000-01-01 02:00 WORKSPACE

When a sanitizer (say, UBSAN via `-fsanitize=undefined`) is turned on, `zig cc` will include absolute paths to some header files, making the artifacts non-reproducible.

This commit strips dirnames from such header files.

Signed-off-by: Motiejus Jakštys <motiejus@uber.com>

See #99

2.19 is no longer relevant, as Jessie is a long-time EOL.

This will reduce test duration as a side-effect.

bazel.slack.com -> bazelbuild.slack.com

And I wondered why on earth I could log in from one, but not the other machine.

Signed-off-by: Motiejus Jakštys <motiejus@uber.com>

The "apt-get install" step in "Test zig utilities" was failing, which
caused the later test to fail.

Turns out buildkite does not add `set -e` on shell scripts, so we gotta
do it.

Co-authored-by: zplin <zplin@uber.com>

Upgrade Bazel, rules_go and Gazelle to their latest version, and also
add
`--experimental_output_directory_naming_scheme=diff_against_baseline`
according to the recommendation of
[rules_go](https://github.com/bazelbuild/rules_go/releases/tag/v0.38.0),
which cut down the CI time by half

Releaser currently does not update MODULE.bazel, thus making the version
specified there out of date.

Now releaser updates MODULE.bazel too. The CI scripts will be updated as
a follow-up.

Fixes #97

---------

Signed-off-by: Zhongpeng Lin <zplin@uber.com>
Co-authored-by: Zhongpeng Lin <zplin@uber.com>
Co-authored-by: Sung Yoon Whang <sungyoonwhang@gmail.com>

This adds the template files so that the Publish to BCR app can publish
new releases of this repo to Bazel Central Repository as Bazel modules.

Zig 0.11.0 is released. Upgrading to the released version exposed some
wrong assumptions about URL format. So this PR also fixed those
assumptions by using `URL_FORMAT_RELEASE` for released version and
determining the mirror URL format from the original one.