x/build: add more race detector builders

[randall77]

We should have one for every supported race detector config.

We currently have:

darwin/amd64
freebsd/amd64
linux/amd64
windows/amd64

We'd need to add:

netbsd/amd64
linux/arm64
linux/ppc64le

@bradfitz

When attempting to rebuild the .syso files as part of #33309 , I ran into these additional platforms where race.bash does not pass, usually because of dumb reasons that would be easily caught and fixed if we had builders for them.

Builders would also be useful to test my fix for #33309 .