[CI] Add test for projects list for .ci on Windows

Partially to give me something to copy and paste into other scripts that
need to run all of the tests on Windows and partially to increase test
coverage on Windows. This does expose an issue with the script on
Windows, so that needs to be fixed. Given it does not impact anything it
should be fine for now though.

.ci/compute_projects_test.py

@@ -284,6 +284,34 @@ class TestComputeProjects(unittest.TestCase):
             "check-cxx check-cxxabi check-unwind",
         )
 
+    def test_windows_ci(self):
+        env_variables = compute_projects.get_env_variables(
+            [".ci/compute_projects.py"], "Windows"
+        )
+        self.assertEqual(
+            env_variables["projects_to_build"],
+            "clang;clang-tools-extra;libclc;lld;llvm;mlir;polly",
+        )
+        self.assertEqual(
+            env_variables["project_check_targets"],
+            "check-clang check-clang-cir check-clang-tools check-lld check-llvm check-mlir check-polly",
+        )
+        self.assertEqual(
+            env_variables["runtimes_to_build"],
+            "libcxx;libcxxabi;libunwind",
+        )
+        self.assertEqual(
+            env_variables["runtimes_check_targets"],
+            "",
+        )
+        # TODO(boomanaiden154): We should not be emitting these on Windows.
+        # It does not currently impact anything because we do not build the
+        # runtimes on Windows though.
+        self.assertEqual(
+            env_variables["runtimes_check_targets_needs_reconfig"],
+            "check-cxx check-cxxabi check-unwind",
+        )
+
     def test_lldb(self):
         env_variables = compute_projects.get_env_variables(
             ["lldb/CMakeLists.txt"], "Linux"