build(deps): bump third_party/vexriscv-verilog (#403)

Bumps [third_party/vexriscv-verilog](https://github.com/m-labs/VexRiscv-verilog) from `ddf348e` to `2e4f43d`.
- [Release notes](https://github.com/m-labs/VexRiscv-verilog/releases)
- [Commits](m-labs/VexRiscv-verilog@ddf348e...2e4f43d)

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

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