By default, go compiles binaries linked to libc to use the system DNS resolver. It does re-implement a DNS resolver but it's only used if CGO is disabled at compilation time.
Use go for what? DNS resolution? The default behavior is to use the system DNS resolver. The Go resolver will be used if the system is resolver is not avaialble (e.g. if the binary is compiled as pure go) or if the net.Resolver has the PreferGo flag set (which is false by default).