added Windows target testing

ci/test

@@ -1,3 +1,13 @@
-#!/bin/sh
+#!/bin/bash
+set -euo pipefail
 
-exec bazel test ...
+bazel test ...
+
+# Windows tests
+# Unfortunately wine-binfmt breaks within the bazel sandbox, so we disable it
+# to run this test.
+bazel test //test/c:winver_windows_amd64 \
+    --spawn_strategy=standalone
+# There is no no easy way to run windows_arm64 binaries on Linux, so we just
+# cross compile one for testing.
+bazel build //test/c:winver_windows_arm64