cmd/upload: use specified go version for building
cmd/upload: use specified go version for building

There's an optional -go flag to specify Go version for compilation.
Use it in both invocations of the "go" command, not just the first.

This is a followup to CL 207420 where the -go flag was added.

Change-Id: Ic33b9acf194fb8fda582d3495e4247fec36218e0
Reviewed-on: https://go-review.googlesource.com/c/build/+/216837
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build