go/types: escape +build sequence to silence vet warning
go/types: escape +build sequence to silence vet warning

Appease the vet builder until we figure out the ideal solution.

Updates #21716.

Change-Id: I64ecdf9b6efb0933c5c79e11c860966ff1980305
Reviewed-on: https://go-review.googlesource.com/60776
Run-TryBot: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

nawawi/go,codestation/go,josharian/go,codestation/go,codestation/go,CAFxX/go,cloudflare/go,golang/go,josharian/go,CAFxX/go,cloudflare/go,Cofyc/go,polyverse-security/go,Cofyc/go,josharian/go,cloudflare/go,codestation/go,polyverse-security/go,josharian/go,golang/go,akutz/go,codestation/go,nawawi/go,CAFxX/go,cloudflare/go,nawawi/go,josharian/go,akutz/go,golang/go,cloudflare/go,nawawi/go,akutz/go,polyverse-security/go,Cofyc/go,nawawi/go,CAFxX/go,josharian/go,polyverse-security/go,polyverse-security/go,CAFxX/go,polyverse-security/go,Cofyc/go,cloudflare/go,CAFxX/go,Cofyc/go,akutz/go,polyverse-security/go,Cofyc/go,polyverse-security/go,nawawi/go,christopher-henderson/Go,josharian/go,nawawi/go,golang/go,josharian/go,golang/go,golang/go,golang/go,cloudflare/go,codestation/go,CAFxX/go,codestation/go,akutz/go,codestation/go,Cofyc/go,akutz/go,golang/go,Cofyc/go,akutz/go,nawawi/go,cloudflare/go,CAFxX/go,akutz/go