Re-enable Go race detector

[q3k]

We currently test without the Go race detector enabled. That's because the Go race detector depends on cgo, and our cgo/musl integration currently doesn't work (as cgo calls our gcc wrapper from a nested directory within execroot, but our gcc wrapper / sysroot makes assumptions that we always run from the execroot).

There might also also be some other complications like the race detector not working with musl - that will have to be investigated.

We could also just enable the race detector for host go_test targets, and nothing else.

[leoluk]

Upstream bugs:

• runtime/race: eliminate dependency on libc golang/go#9918
• runtime/race: eliminate dependency on cmd/cgo golang/go#6508

[q3k]

We should at least re-enable it when running host tests, which shouldn't depend on the above two bugs being fixed.

[q3k]

Letting someone else deal with this. This will either require waiting for the Go race detector to work without CGO, or getting CGO to work.

There's some early work in https://review.monogon.dev/c/monogon/+/1833 ; good luck.

[fionera]

This is done.