build varlink without GOPATH
when gopath was not explicitly set, make would fail due
to the varlink generator.  this symlink in the makefile
addresses that.
fixes:
@@ -94,6 +94,7 @@ help:
ifeq ("$(wildcard $(GOPKGDIR))","")
mkdir -p "$(GOPKGBASEDIR)"
ln -sf "$(CURDIR)" "$(GOPKGBASEDIR)"
+ ln -sf "$(CURDIR)/vendor/github.com/varlink" "$(FIRST_GOPATH)/src/github.com/varlink"
endif
touch $@
