go-fuzz-build: respect GO111MODULE if set

This is an alternative to dvyukov#271.

Updates dvyukov#195

go-fuzz-build/main.go

@@ -60,7 +60,12 @@ func makeTags() string {
 // that clients can then modify and use for calls to go/packages.
 func basePackagesConfig() *packages.Config {
  cfg := new(packages.Config)
- cfg.Env = append(os.Environ(), "GO111MODULE=off")
+ // Until we have proper module support, disable modules.
+ // However, if a user has explicitly set GO111MODULE,
+ // assume they know what they're doing, and respect it.
+ if _, ok := os.LookupEnv("GO111MODULE"); !ok {
+ cfg.Env = append(os.Environ(), "GO111MODULE=off")
+ }
  return cfg
 }