cmd/go/internal/test: data race in (*runCache).builderRunTest [1.13 backport] #38082
Description
@bcmills requested issue #38077 to be considered for backport to the next 1.13 minor release.
@gopherbot, please backport to Go 1.13 and 1.14. This is a data race in
cmd/go, and data races can lead to arbitrary memory corruption.