cmd/godoc: add x/arch repo to list
cmd/godoc: add x/arch repo to list

Fixes golang/go#12393

Change-Id: I0b56c36dec11a6c2fddcc092867f24701815dce3
Reviewed-on: https://go-review.googlesource.com/14145
Reviewed-by: Dave Cheney <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@cheney.net>

syreclabs/go-tools,syreclabs/go-tools,cmars/tools,golang/tools,syreclabs/go-tools,cmars/tools,syreclabs/go-tools,magiccao/tools,cw2018/tools,magiccao/tools,jdhenke/tools,cmars/tools,syreclabs/go-tools,runcom/tools,syreclabs/go-tools,magiccao/tools,cw2018/tools,jdhenke/tools,runcom/tools,cw2018/tools,cmars/tools,cw2018/tools,golang/tools,jdhenke/tools,jdhenke/tools,runcom/tools,magiccao/tools,golang/tools,golang/tools,golang/tools,runcom/tools