(teleproxy) _go-common.mk: Behave properly if GOPATH is set in the environment
(teleproxy) _go-common.mk: Behave properly if GOPATH is set in the environment

Our overriding GOPATH doesn't affect the $(shell).

This is only tested with go-workspace.mk, not go-mod.mk

datawire/ambassador,datawire/ambassador,datawire/ambassador,datawire/ambassador,datawire/ambassador