ci: produce zip as artifact in Azure Pipelines

Zip files are far more often used on Windows systems, so we provide zip
files in releases. Unfortunately, previously the provided artifact in CI
was really just a compressed .tar.gz file, which defeats the purpose.

This commit zips the release tarball itself so it can be downloaded as
an artifact.

azure-pipelines.yml

@@ -61,9 +61,9 @@ jobs:
           export PATH="/c/Go1.13/bin:$PATH:./llvm-build/bin:/c/Program Files/qemu"
           unset GOROOT
           make release -j4
-    - publish: $(System.DefaultWorkingDirectory)/build/release.tar.gz
-      displayName: Publish tarball as artifact
-      artifact: tinygo.windows-amd64.tar.gz
+    - publish: $(System.DefaultWorkingDirectory)/build/release/tinygo
+      displayName: Publish zip as artifact
+      artifact: tinygo
     - task: Bash@3
       displayName: Smoke tests
       inputs: