Added verilator_toolchain rule.

[abrisco]

This change adds a verilator_toolchain rule that can be used to share Verilator inputs to compile actions across different rules.

[abrisco]

@QuantamHD I'm not sure why this one is failing, there's no logs I can see 😞

[QuantamHD]

Looks like a flag parsing issue.

5c57b-bd91-49bf-982e-b5a172618b07"

FETCHSOURCE
hint: Using 'master' as the name for the initial branch. This default branch name
hint: is subject to change. To configure the initial branch name to use in all
hint: of your new repositories, which will suppress this warning, call:
hint: 
hint: 	git config --global init.defaultBranch <name>
hint: 
hint: Names commonly chosen instead of 'master' are 'main', 'trunk' and
hint: 'development'. The just-created branch can be renamed via this command:
hint: 
hint: 	git branch -m <name>
Initialized empty Git repository in /workspace/.git/
From https://github.com/hdl/bazel_rules_hdl
 * branch            21e195363892c6f4855122c4a31859f1876fdd38 -> FETCH_HEAD
HEAD is now at 21e1953 Added `verilator_toolchain` rule.
BUILD
Starting Step #0
Step #0: Already have image (with digest): gcr.io/cloud-builders/gcloud
Finished Step #0
Starting Step #1
Step #1: Already have image (with digest): gcr.io/cloud-builders/bazel
Step #1: STATUS: Reporting logs with build invocation id ddc4f0a8-0fd7-11ef-ba07-0242c0a80a02 and test invocation id ddcaa516-0fd7-11ef-b819-0242c0a80a02 to GitHub.
Step #1: Extracting Bazel installation...
Step #1: Starting local Bazel server and connecting to it...
Step #1: INFO: Reading rc options for 'run' from /workspace/.bazelrc:
Step #1:   Inherited 'common' options: --noenable_bzlmod
Step #1: ERROR: --noenable_bzlmod :: Unrecognized option: --noenable_bzlmod
Finished Step #1
ERROR
ERROR: build step 1 "gcr.io/cloud-builders/bazel" failed: step exited with non-zero status: 2

[abrisco]

@QuantamHD Updated!