toolchain: Upload fatal clang warning logs

We need to upload fatal clang warnings logs for our tools to
auto-detect and alert toolchain mage. This patch ports a temporary
CL in legacy builder (crrev.com/c/1790389) into recipe world.

Also add a new handler in the API controller.

BUG=chromium:1077363
TEST=CQ

Change-Id: I550187ffd3857e9eec07d4e8d9490e5dc21ce473
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2199655
Tested-by: Tiancong Wang <tcwang@google.com>
Reviewed-by: LaMont Jones <lamontjones@chromium.org>
Commit-Queue: Tiancong Wang <tcwang@google.com>
diff --git a/api/controller/toolchain.py b/api/controller/toolchain.py
index 7d5a236..9b72c23 100644
--- a/api/controller/toolchain.py
+++ b/api/controller/toolchain.py
@@ -70,6 +70,9 @@
     BuilderConfig.Artifacts.VERIFIED_RELEASE_AFDO_FILE:
         _Handlers('VerifiedReleaseAfdoFile', toolchain_util.PrepareForBuild,
                   toolchain_util.BundleArtifacts),
+    BuilderConfig.Artifacts.TOOLCHAIN_WARNING_LOGS:
+        _Handlers('ToolchainWarningLogs', toolchain_util.PrepareForBuild,
+                  toolchain_util.BundleArtifacts),
 }