Bump external/OpenCL-Headers from 542d7a8 to 4ea6df1

Bumps [external/OpenCL-Headers](https://github.com/KhronosGroup/OpenCL-Headers) from `542d7a8` to `4ea6df1`.
- [Release notes](https://github.com/KhronosGroup/OpenCL-Headers/releases)
- [Commits](KhronosGroup/OpenCL-Headers@542d7a8...4ea6df1)

---
updated-dependencies:
- dependency-name: external/OpenCL-Headers
  dependency-type: direct:production
...

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