cmd/compile: document -trimpath
cmd/compile: document -trimpath

Fixes #8999.

Change-Id: I1390605bdf908f59b596975ea51eb04bd03bbae0
Reviewed-on: https://go-review.googlesource.com/16918
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

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