foundation: stage1 - gnutar: make build scripts executable

[srd424]

mescc-tools-extra's 'untar' tool doesn't set file modes at all, so scripts like missing are not immediately executable

Hydra failure log: https://hydra.aux-cache.dev/build/45/nixlog/1/tail

mescc-tools-extra's untar source (I think): https://github.com/oriansj/mescc-tools-extra/blob/master/untar.c#L139

[jakehamilton]

I'll try and take a look at this a bit later, thanks!

[srd424]

Yeah, not sure why you didn't hit it - possibly you had something cached locally that had been built some other way? Either that or there's something weird about the hydra environment (well, even weirder than we already know!)