Add an additional bazelrc file for Windows.

This is a workaround for the path-length issue on building protobuf on
Windows with bazel.

 * protocolbuffers/protobuf#12947
 * bazelbuild/bazel#18683

To work around it, specify --bazelrc=windows.bazelrc as follows.

  bazel --bazelrc=windows.bazelrc   \
        build //protocol:commands_proto  \
        --config oss_windows

This is a preparation to support Bazel for Windows build (#948).

There must be no observable behavior change in mac/Linux Bazel builds.

PiperOrigin-RevId: 645622326

src/windows.bazelrc

@@ -0,0 +1,15 @@
+# Currently there seems to be no way to customize startup option based on the
+# host platform.
+# https://github.com/bazelbuild/bazel/issues/22763
+# Thus having our own file here.
+# To specify this file, use the "-bazelrc" option as follows.
+#
+#   bazel --bazelrc=windows.bazelrc build //protocol:commands_proto \
+#         --config oss_windows
+
+# There has been a long standing path-length issue on building protobuf on
+# Windows with bazel. See the following for details.
+# https://github.com/protocolbuffers/protobuf/issues/12947
+# https://github.com/bazelbuild/bazel/issues/18683
+# Here is an ugly workaround, which we really hope to get rid of.
+startup  --output_base=C:/x --windows_enable_symlinks