cipd needs modifications to build natively

[ghost]

Describe the bug
The native build of v8 relies on Google's depot_tools, including cipd. I have made changes here to add riscv64 to the case statement, but further changes are still required.

To Reproduce
Steps to reproduce the behavior:

1. Start RISC-V simulation in QEMU (probably the same behavior on the board, but I have not tested)
2. Clone the modified depot_tools: git clone https://github.com/v8-riscv/depot_tools.git
3. Add depot_tools to PATH: export PATH=/path/to/depot_tools:$PATH
4. Test using gclient
5. See error

Errors/Logs

Platform linux-riscv64 is not supported by the CIPD client bootstrap: there's no pinned SHA256 hash for it in the *.digests file.
/root/depot_tools/bootstrap_python3: line 32: bootstrap-3.8.0.chromium.8_bin/python3/bin/python3: No such file or directory
cat: /root/depot_tools/python3_bin_reldir.txt: No such file or directory
/root/depot_tools/vpython3: line 52: /root/depot_tools/.cipd_bin/vpython3: No such file or directory

Additional context
It is unclear if we would be responsible for the changes to depot_tools or if Google would handle that. I have asked them via email.