Fixing bazel-to-cmake regression that broke it on Windows. (#4981)

diff --git a/build_tools/bazel_to_cmake/bazel_to_cmake.py b/build_tools/bazel_to_cmake/bazel_to_cmake.py
index 2d1e429..e938272 100755
--- a/build_tools/bazel_to_cmake/bazel_to_cmake.py
+++ b/build_tools/bazel_to_cmake/bazel_to_cmake.py
@@ -109,7 +109,7 @@
 
 
 def repo_relpath(path):
-  return os.path.relpath(path, repo_root)
+  return os.path.relpath(path, repo_root).replace("\\", "/")
 
 
 def log(string, *args, indent=0, **kwargs):