If I disable optimizations (-N option for go tool compile), the error disappears. I think this confirms it is a compiler bug.
$ GOPATH=$PWD/build go test -c -v -gcflags=-N github.com/prometheus/prometheus/storage/local $ GOPATH=$PWD/build go test -c -v github.com/prometheus/prometheus/storage/local # github.com/prometheus/prometheus/storage/local build/src/github.com/prometheus/prometheus/storage/local/storage_test.go:2028:26: invalid instruction: 01483 (/tmp/buildd/prometheus-1.8.1+ds/build/src/github.com/prometheus/prometheus/storage/local/storage_test.go:2029) FMOVD ""..autotmp_78+176(DX)(SP*1), F0 $
