run.bash: GOPATH should be set to a non-existent, non-empty string

[sean-jc]

Various tests invoked by run.bash fail if $GOROOT resides under $GOPATH. run.bash previously handled this via unset GOPATH prior to running the tests, but this is no longer sufficient as Go now defines a default $GOPATH (#17262), i.e $GOROOT may conflict with the default $GOPATH. This can be resolved by setting GOPATH to a semantically valid, non-empty string that is guaranteed not to conflict with $GOROOT, e.g. GOPATH=$GOROOT/nil.

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What version of Go are you using (go version)?

1.8, or any build since dc4a815.

What operating system and processor architecture are you using (go env)?

go env

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/sean/go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build456320300=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"

What did you do?

Clone go repository to /home/sean/go/src/github.com/golang/go, run all.bash.

What did you expect to see?

Successful build.

What did you see instead?

cgo tests that import local packages fail, e.g. gcc68255.go:10:2: local import "./gcc68255" in non-local package.

[gopherbot]

CL https://golang.org/cl/37396 mentions this issue.