build(deps): bump third_party/gflags from 03a4842 to 3c4399b

Bumps [third_party/gflags](https://github.com/gflags/gflags) from `03a4842` to `3c4399b`.
- [Release notes](https://github.com/gflags/gflags/releases)
- [Commits](gflags/gflags@03a4842...3c4399b)

---
updated-dependencies:
- dependency-name: third_party/gflags
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>