cmd/dist: show output from failed compiler execution
cmd/dist: show output from failed compiler execution

Maybe it will say something that helps the user understand the problem.

Note that we can't use os/exec.ExitError's new Stderr field because
cmd/dist is compiled with Go 1.4.

Fixes #13099.

Change-Id: I4b5910434bf324d1b85107002a64684d8ba14dc8
Reviewed-on: https://go-review.googlesource.com/17940
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

momchil-velikov/go,derekmarcotte/go,mwhudson/go,josharian/go,suncycheng/go,roth1002/go,ImJasonH/go,Endika/go,linux-on-ibm-z/go,akutz/go,cloudflare/go,ganboing/go-esx,CAFxX/go,binarycrusader/go,vsekhar/elastic-go,ganboing/go-esx,akutz/go,nawawi/go,derekmarcotte/go,golang/go,4ad/go,nawawi/go,codestation/go,CAFxX/go,golang/go,Samurais/go,vsekhar/elastic-go,cyberroadie/go,polyverse-security/go,roth1002/go,ganboing/go-esx,momchil-velikov/go,Samurais/go,sndnvaps/go,golang/go,roth1002/go,derekmarcotte/go,momchil-velikov/go,CAFxX/go,vsekhar/elastic-go,kim-racktop/go,Endika/go,polyverse-security/go,cyberroadie/go,momchil-velikov/go,cyberroadie/go,deft-code/go,ImJasonH/go,golang/go,akutz/go,suncycheng/go,josharian/go,roth1002/go,polyverse-security/go,cyberroadie/go,josharian/go,binarycrusader/go,roth1002/go,miolini/go,goodlang/good,codestation/go,josharian/go,sndnvaps/go,Endika/go,josharian/go,mwhudson/go,linux-on-ibm-z/go,ganboing/go-esx,miolini/go,derekmarcotte/go,Cofyc/go,cyberroadie/go,binarycrusader/go,binarycrusader/go,binarycrusader/go,nawawi/go,roth1002/go,vsekhar/elastic-go,binarycrusader/go,momchil-velikov/go,kim-racktop/go,Endika/go,cloudflare/go,linux-on-ibm-z/go,Samurais/go,sndnvaps/go,CAFxX/go,theif519/go,kim-racktop/go,derekmarcotte/go,cloudflare/go,4ad/go,vanloswang/go,christopher-henderson/Go,nawawi/go,polyverse-security/go,akutz/go,vanloswang/go,vsekhar/elastic-go,theif519/go,josharian/go,goodlang/good,linux-on-ibm-z/go,Cofyc/go,suncycheng/go,theif519/go,momchil-velikov/go,kim-racktop/go,suncycheng/go,vanloswang/go,4ad/go,Samurais/go,goodlang/good,Endika/go,CAFxX/go,cloudflare/go,Cofyc/go,nawawi/go,vanloswang/go,sndnvaps/go,mwhudson/go,Samurais/go,josharian/go,akutz/go,Endika/go,miolini/go,linux-on-ibm-z/go,deft-code/go,suncycheng/go,cloudflare/go,deft-code/go,codestation/go,mwhudson/go,akutz/go,deft-code/go,Cofyc/go,ImJasonH/go,ImJasonH/go,goodlang/good,vsekhar/elastic-go,CAFxX/go,miolini/go,suncycheng/go,golang/go,nawawi/go,goodlang/good,mwhudson/go,cloudflare/go,momchil-velikov/go,polyverse-security/go,Cofyc/go,suncycheng/go,deft-code/go,sndnvaps/go,ganboing/go-esx,roth1002/go,ImJasonH/go,suncycheng/go,derekmarcotte/go,linux-on-ibm-z/go,derekmarcotte/go,goodlang/good,theif519/go,cyberroadie/go,cloudflare/go,Samurais/go,4ad/go,golang/go,vanloswang/go,cloudflare/go,golang/go,ImJasonH/go,CAFxX/go,codestation/go,nawawi/go,codestation/go,kim-racktop/go,theif519/go,goodlang/good,codestation/go,4ad/go,golang/go,akutz/go,CAFxX/go,sndnvaps/go,sndnvaps/go,theif519/go,mwhudson/go,miolini/go,cyberroadie/go,miolini/go,kim-racktop/go,Cofyc/go,cyberroadie/go,miolini/go,kim-racktop/go,codestation/go,polyverse-security/go,mwhudson/go,vanloswang/go,deft-code/go,polyverse-security/go,ganboing/go-esx,ganboing/go-esx,sndnvaps/go,linux-on-ibm-z/go,4ad/go,akutz/go,nawawi/go,vsekhar/elastic-go,deft-code/go,ImJasonH/go,binarycrusader/go,kim-racktop/go,theif519/go,josharian/go,Cofyc/go,linux-on-ibm-z/go,4ad/go,momchil-velikov/go,Endika/go,binarycrusader/go,ganboing/go-esx,ImJasonH/go,Cofyc/go,polyverse-security/go,vsekhar/elastic-go,4ad/go,Samurais/go,roth1002/go,Endika/go,vanloswang/go,derekmarcotte/go,goodlang/good,vanloswang/go,mwhudson/go,theif519/go,codestation/go,deft-code/go,Samurais/go,miolini/go