Support setting GOAMD64

[peterebden]

This adds a config setting allowing overriding the AMD64 target.

Have tested flipping back and forth between v1 and v3 and it seems fine (once I added the env var to everything)

[peterebden]

Hmmmm. Seeing some odd behaviour with go_repo where it doesn't always seem to recompile things (although I think it should since the libraries clearly seem to change with the config value)

[Tatskaari]

Hmmmm. Seeing some odd behaviour with go_repo where it doesn't always seem to recompile things (although I think it should since the libraries clearly seem to change with the config value)

Oh really? Was it the go_librarys in the subrepos that weren't re-building? I haven't noticed anything like that... do you think it might be something to do with the config option not being inherited?

[peterebden]

Hmmmm. Seeing some odd behaviour with go_repo where it doesn't always seem to recompile things (although I think it should since the libraries clearly seem to change with the config value)

Oh really? Was it the go_librarys in the subrepos that weren't re-building? I haven't noticed anything like that... do you think it might be something to do with the config option not being inherited?

I was getting some error about ABI mismatching because this was different. It seemed like it must be something not inhering somewhere, or something along those lines, but didn't get to the bottom of it.