Strip the zig-builder binary for reproducibility

[dzbarsky]

Prior to this, I noticed builds ending up with different digests for the builder fairly often. Stripping those builder binaries manually made them match up; with this patch applied, I was able to have builds be 100% cached when trying 5 times (previously almost every time was a different digest).

[CLAassistant]

All committers have signed the CLA.

[motiejus]

Did you validate it does become reproducible after this change? Please update the commit message with more details.

Code-wise lgtm

[dzbarsky]

Yes, it looks reproducible to me; updated the summary.

[motiejus]

Yes, it looks reproducible to me; updated the summary.

This is good, thanks. Please rebase and add the description to the commit.

I noticed the release tests are broken, at some point we will take action on those. I cannot make any concrete time promises, but we will get to it.

[motiejus]

Thanks!