cmd/dist: skip rebuild before running tests when on the build systems
cmd/dist: skip rebuild before running tests when on the build systems

Updates #24300

Change-Id: I7752dab67e15a6dfe5fffe5b5ccbf3373bbc2c13
Reviewed-on: https://go-review.googlesource.com/99296
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

nawawi/go,josharian/go,codestation/go,cloudflare/go,golang/go,nawawi/go,josharian/go,golang/go,golang/go,codestation/go,akutz/go,Cofyc/go,Cofyc/go,cloudflare/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,akutz/go,akutz/go,codestation/go,codestation/go,nawawi/go,codestation/go,cloudflare/go,josharian/go,Cofyc/go,cloudflare/go,CAFxX/go,Cofyc/go,cloudflare/go,josharian/go,cloudflare/go,codestation/go,nawawi/go,nawawi/go,Cofyc/go,nawawi/go,golang/go,cloudflare/go,josharian/go,nawawi/go,codestation/go,golang/go,akutz/go,akutz/go,golang/go,josharian/go,CAFxX/go,josharian/go,CAFxX/go,golang/go,Cofyc/go,josharian/go,CAFxX/go,akutz/go,cloudflare/go,Cofyc/go,akutz/go,akutz/go,CAFxX/go,codestation/go,CAFxX/go,Cofyc/go