cgo: do not pass cgoLDFLAGS to cmd/cgo directly
cgo: do not pass cgoLDFLAGS to cmd/cgo directly

Updates #331 (doesn't fix it, just makes it blow up less)

hyper-carrot/gb,mopemope/gb,hyper-carrot/gb,mopemope/gb,tbruyelle/gb,tianon/gb,constabulary/gb,ches/gb,lparkes/gb,constabulary/gb,tianon/gb,constabulary/gb,davidkaya/gb,tbruyelle/gb,inconshreveable/gb,ches/gb,mopemope/gb,inconshreveable/gb,davidkaya/gb