test-wrapper: add empty impl + Bazel flag

This commit adds:

- the skeleton implementation of the Windows
  native test wrapper

- a depenency on the native test wrapper from test
  rules, through the new $test_wrapper rule
  attribute

- the --windows_native_test_wrapper Bazel flag,
  which is currently a no-op

See https://github.com/bazelbuild/bazel/issues/5508

Change-Id: I8df95c8ce8bab53c51c257698ec95416065a836e

Closes #5854.

Change-Id: I2ffc78bceec5dd867af775b5878f105fa87c3dba
PiperOrigin-RevId: 208650699
diff --git a/tools/test/BUILD.tools b/tools/test/BUILD.tools
index 5e4e5f55d..c41e293 100644
--- a/tools/test/BUILD.tools
+++ b/tools/test/BUILD.tools
@@ -32,3 +32,11 @@
     name = "coverage_report_generator",
     srcs = ["@bazel_tools//tools/test/LcovMerger/java/com/google/devtools/lcovmerger:Main"],
 )
+
+filegroup(
+    name = "test_wrapper",
+    srcs = select({
+        "@bazel_tools//src/conditions:windows": ["test_wrapper_bin.exe"],
+        "//conditions:default": ["test_wrapper_bin"],
+    }),
+)