Introduce a stub bazel_wrapper/bazel.bat

This is a preparation before starting using 'clang-cl' to build Mozc for
for Windows with Bazel (google#1179).

In order to make the build process reliable and reproducible, we would
like to download a specific version of LLVM with 'update_deps.py' then
deploy it under 'third_party/llvm/' and let 'rules_cc' use it by
specifying 'BAZEL_LLVM' environment variable [1].

To automate this process, one idea is to use 'tools/bazel' wrapper
script [2]. Luckily the wrapper script directory is also customizable
since bazelisk v1.21.0 [3].

With above this commit introduces a stub 'bazel.bat' so that we can use
it to set various environment variables for Windows bazel build in
subsequent commits. At this moment there must be no difference in the
final artifacts.

 [1]: https://bazel.build/configure/windows#clang
 [2]: https://github.com/bazelbuild/bazelisk/blob/master/README.md#toolsbazel
 [3]: bazelbuild/bazelisk#567

src/.bazeliskrc

@@ -1 +1,2 @@
 USE_BAZEL_VERSION=8.1.0
+BAZELISK_WRAPPER_DIRECTORY=./bazel_wrapper

src/bazel_wrapper/README.md

@@ -0,0 +1,13 @@
+# bazel_wrapper
+
+This directory can be used to place special wrapper scripts for bazelisk.
+
+ * [tools/bazel - Bazelisk](https://github.com/bazelbuild/bazelisk/blob/master/README.md#toolsbazel).
+
+By default `bazel` and `bazelisk` uses `tools/` as the bazel wrapper directory, but `bazelisk` allows us to customize it with `BAZELISK_WRAPPER_DIRECTORY` in [`src/.bazeliskrc`](../.bazeliskrc) since bazelisk v1.21.0.
+
+ * [Allow overriding tools/bazel path with BAZELISK_WRAPPER_DIRECTORY](https://github.com/bazelbuild/bazelisk/pull/567)
+
+## Contents
+
+ * [bazel.bat](./bazel.bat)

src/bazel_wrapper/bazel.bat

@@ -0,0 +1,5 @@
+@echo off
+%BAZEL_REAL% %* & call:myexit
+
+:myexit
+exit /b